Presidential Data Archive:

Support Score Explanation Page

The following is a description of presidential support scores as coded and calculated in:

Edwards, George C., III. 1989. At the Margins: Presidential Leadership of Congress. New Haven: Yale University Press. Chapter 2.

Overall Support

The most inclusive index of presidential success in Congress is Overall Support, which includes all the votes on which the president has taken a stand. The basis for determining these issues is the yearly almanac of Congressional Quarterly (CQ). CQ analyzes all the public statements and messages of the president to determine what legislation he desires or does not desire. Only issues on which the president has taken a stand are included in the indexes, and CQ includes votes only if the legislation that the president originally supported is voted on in a similar form: bills are excluded if they have been so extensively amended that a vote can no longer be characterized as reflecting support for the president or opposition to him. The position of the president at the time of the vote is the basis for measuring support or opposition in cases where his position has changed before or after the vote. Key votes to recommit, reconsider, or table legislation are included, but appropriations bills are included only if they deal with specific funds that the president requested be added or deleted. This last distinction helps keep the measure one of support for the president rather than for the institutionalized presidency.

Although I rely on the judgments of CQ in determining the issues on which the president has taken a stand, I have not simply adopted the Presidential Support Scores of CQ. The index of Overall Support was coded independently, owing partly to occasional errors in the calculations of CQ, partly due to the deletion by CQ of certain votes pertaining to the Civil Rights Act of 1964, and partly to my handling of paired votes (discussed below).

There are drawbacks as well as advantages to an index that measures the support of members of Congress on all the votes on which the president has taken a stand. Such an index may include lopsided votes and many votes on the same issue, and it weighs all issues equally. More restrictive indexes of presidential support do not have these limitations.

There is no evidence that presidents have varied in their use of posturing, that is, trying to inflate their degree of congressional support by proposing popular but frivolous legislation or by withholding unpopular legislation. Although some instances of each device have undoubtedly occurred, there seem to be no systematic differences in the degree to which presidents have employed them.

Nonunanimous Support

Because many of the issues on which the president takes a stand are not controversial and are decided by nearly unanimous votes, including them in a measure of support for the president can distort the results by inflating the measure. Further, the number of these votes varies over time, and including them in a measure of presidential support can therefore frustrate attempts to correlate the measure with possible explanatory variables. Comparisons between the House and Senate may also be distorted if these votes are included, because the Senate tends to have more unanimous votes, owing at least in part to its special responsibilities for confirming appointments and ratifying treaties, most of which are not controversial.

To avoid the problem of unanimous votes, I employ the measure Nonunanimous Support, an index of support for the president in votes on which the winning side numbered less than 80 percent of those who voted. Although this figure is somewhat arbitrary, it is a reasonable cutoff, beyond which presidential influence appears to be largely irrelevant. It is worthwhile to note that there are many instances of nearly unanimous votes that the president lost. Evidently the president felt it necessary in these cases to take a principled stand against hopeless odds. A drawback to the measure Nonunanimous Support is that the overwhelming consensus on an issue may be due to the president's influence. Thus when we omit unanimous and nearly unanimous votes from an index of presidential support, we may lose useful information.

Single-Vote Support

Very often there are many roll-call votes on the same issue. In some cases there are a dozen or more on one bill, as amendment after amendment is decided by roll-call vote. In the most extreme case, the Senate took 116 roll-call votes on the Civil Rights Act of 1964. When one issue provides a large percentage of the votes on which the president took a stand, the potential for distortion is obvious. The resulting index will be biased toward both the president's influence and the broader configuration of forces at work on the one issue.

The index Single-Vote Support avoids this problem. This is an index of support for the president on the most important nonunanimous vote on each bill. There is only one vote per bill in this index. If a key vote was designated for an issue, this is the vote used; if there were two key votes and one was on final passage, the index uses the latter; if there were two key votes and neither was on final passage, the one with the closest vote is used, on the theory that close votes are the best tests of the president's influence. Typically, no key vote is designated by Congressional Quarterly. In such cases the first choice is the vote on final passage of the bill. If this is not available, the most closely contested remaining vote is used.

There is no objective way to determine the most important vote on a bill. Although passage is often the crucial vote, at other times hotly contested amendments or even procedural votes may be more significant. By choosing among amendments on the basis of how closely contested they were, there is the possibility of choosing votes on which the president was less successful and excluding votes on which he was more so; one simply cannot tell. Finally, a few bills cover several disparate issues. For example, consideration of the continuing appropriations bill of fiscal 1983 in the Senate included votes on the MX missile, the Clinch River breeder reactor, licensing of professions by the Federal Trade Commission, public works jobs, social security benefits, abortion funding, and funds for Central American guerrillas. Excluding multiple votes on the same issue thus avoids and creates problems in measuring presidential support.

Note: single-vote support scores are not calculated after 1994.

Key Votes

Each year Congressional Quarterly selects key votes that occurred in each house during the session. A key vote is one or more of the following: a matter of major controversy, a test of presidential or political power, and a decision of potentially great impact on the nation and on lives of Americans. A measure of presidential support relying on key votes is attractive because these votes represent only significant issues, and thus help to avoid distorting measurements of presidential success with less important ones. It is possible that a president's success on relatively inconsequential issues may mask his failure to obtain support on more important ones.

Nevertheless, there are several reasons to exercise caution in the use of key votes. First, the president does not take a stand on all of them. Over the thirty-four years covered here, the president took a stand on 72 percent of the key votes in the House and 66 percent in the Senate, and from 1969 only on 60 percent and 56 percent. Second, in 7 percent of the key votes in the House and 11 percent in the Senate the winning side included at least 80 percent of the legislators who voted, and these votes may therefore not be a useful test of presidential influence. Third, the number of key votes on which the president has taken a stand is very small: the yearly average is ten in the House and nine in the Senate. This is a very modest basis for generalizations about presidential leadership of Congress. Fourth, there is sometimes more than one key vote on a single issue (for example, four of ten key votes in the House in 1985 were on one issue).

Finally, although weighing votes equally may mask important information, it also has certain advantages. What appear to be the most significant votes are not necessarily the best tests of presidential influence or leadership. Even if we know the president's complete set of priorities (which we do not), and even if he has a comprehensive set of priorities (which he often does not), each member of Congress responds to presidential requests with his or her own set of priorities (to the degree that the member has one). One cannot assume that the issues the president cares about most and therefore fights for the hardest are those that members of Congress care about most, and for this reason we cannot assume that these issues are the best tests of presidential influence. The president's task in such cases is not necessarily especially difficult, as the occasional nearly unanimous results on key votes indicate.

Another reason why the varying degrees of presidential effort to influence Congress may not be a particularly serious problem is that the direct involvement of the president and his staff is only one of several potential sources of influence. A number of others, such as public approval and party affiliation, are not manipulable on a given issue but may be important influences on congressional voting. Further, legislative activities of the White House are frequently strategic rather than tactical, aimed at generating goodwill and not at gaining a particular person's vote on a particular issue. Thus it should not be assumed that a president's tactical efforts are dominant in determining congressional votes.


Calculating each of the four measures involved a massive gathering of data. I first examined each of the several thousand roll calls taken in the House and Senate during the period 1953-86 to identify those on which the president had taken a stand, those on which 80 percent or more of the voting members were on one side, those that were on the same issue, and those that were key votes.

The next step was to calculate the percentage of support each member of Congress gave the president on the votes represented in each measure in each year. To arrive at these percentages I divided the number of times a member of Congress voted or announced a pair for the president's position by the number of stands the president took. These calculations produced over seventy-two thousand index scores.

The Indexes in Perspective

Because of their individual limitations, one should be hesitant in selecting any one index as the only dependent variable for studying presidential leadership in Congress, but rather employ more than one. Using more than one measure provides a more complete picture of presidential support, increases the probability of our understanding presidential leadership, and allows us to identify the types of votes that correlate most highly with different independent variables.

In addition to their individual limitations, the indexes also have some problems in common. They are based solely on roll calls, yet many important decisions are made in committee and on other types of votes. Although there is evidence that roll calls reflect less visible decisions,10 it is not certain that this is so. Nevertheless, roll calls typically occur on a wide range of significant issues and are worthy of study in and of themselves, and roll calls are the only systematic data available on the decisions of the individual members of Congress. The results of studying roll calls also guide us in evaluating presidential legislative strategies such as the setting of the agenda.

Another problem is nonvoting. Support scores are lowered by the absences of members of Congress, most of which are due to illness or official business, but some of which occur when members of Congress desire to support or oppose the president but not to express their positions publicly. Because there is no way to know how to interpret absences, we are forced to assume that the reasons for nonvoting balance out and are evenly distributed throughout each house. This assumption is probably safe, because members from each region have similar rates of voting participation on these sets of roll calls. Moreover, those unable to vote because of prolonged illness, death, or resignation were eliminated from the analysis. Anyone taking part in fewer than 50 percent of the votes in the Overall Support Index was deleted. Unlike Congressional Quarterly, I counted announced pairs in the same way as votes, because they have the same effect. This also gives a more accurate view of presidential support.

Each of the four indexes produces a score for each member of Congress in each year rather than a yearly aggregate for each house or the entire Congress. The indexes make it possible to measure the level of support for a president's program provided by each representative and senator or by any group of them.

For more information see:

Edwards, George C., III. 1989. At the Margins: Presidential Leadership of Congress. New Haven: Yale University Press. Chapter 2.