Party Unity and a catalyst to reduce vote significance

Updated: Nov 10

In our article, Preventing the 2021 U.S. Capitol attack, we assert that an otherwise well-intentioned 1972 political rule change has since made a significant vote weakening impact:

"Resulting from the 1972 McGovern-Fraser Commission recommendations, the state primary and caucus candidate selection system replaced the party insider candidate selection process. This candidate selection change was intended to provide a more democratic candidate selection process. It also enabled an unanticipated and powerful incentive for political parties to reduce vote significance."

But what evidence is there that the 1972 candidate selection rules change actually impacted how lawmakers vote or changed related lawmaker behavior? Also, how does the evidence show more party-line or party unity voting?

This article demonstrates the impact of the 1972 McGovern-Fraser Commission candidate selection recommendation-based rules change. By observing the positive data relationship and increasing data correlations with party unity voting, the analysis shows increasing lawmaker party unity voting since the McGovern-Fraser rule change.

Legislative History and Bipartisanship

Historically, major legislation based on significant societal need has been more likely to receive bipartisan support across political parties. For example,

  • the 1964 law authorizing the Civil Right Act, a program preventing discrimination in public affairs and federally-assisted programs, received 64% Democratic party-based legislative support and 80% Republican party-based legislative support. (1)

  • the 1965 law authorizing Medicare, a medical care program for older Americans, received 84% Democratic party-based legislative support and 49% Republican party-based legislative support. (2)

More recently, major legislation has been less likely to receive bipartisan support. Today lawmakers are more likely to vote along party lines, also known as "party unity" voting. For example,

  • the 2010 law authorizing Affordable Care Act, a program providing medical insurance coverage for most Americans, received 89% Democratic party-based legislative support and 0% Republican party-based legislative support. (3)

While these are notable examples, the questions are:

  1. When did the decline in bipartisanship occur? What was the catalyst that changed how lawmakers vote?

  2. Across all legislation, how powerful is this catalyst?

Our belief is, 1972 McGovern-Fraser Commission candidate selection rules change is that catalyst. But first, here is a summary of the McGovern-Fraser Commission recommendation.

McGovern-Fraser Commission Background

Before 1972, presidential candidates were chosen by party insiders. This process was shrouded in mystery. In 1972 and owing to the McGovern-Fraser Commission recommendations, the more transparent primary and caucus system was enacted to select candidates:

“The McGovern-Fraser Commission issued a set of recommendations that the two parties adopted before the 1972 election. What emerged was a system of binding presidential primaries. Beginning in 1972, the vast majority of the delegates to both the Democratic and Republican conventions would be elected in state-level primaries and caucuses.”

- from How Democracies Die, Levitsky and Ziblatt

About 50 years ago these new rules had an unanticipated impact. That is, party gatekeeping was diminished by placing candidate selection in the hands of the electorate. This is a double-edged sword, while decreasing the party's ability to cut backroom deals, it also reduced their overall ability to act as a gatekeeper. Party gatekeeping is typically used to filter candidates unfit for office. Ironically, this change also increased the political party incentive to manipulate voting rules to tilt power, since the “backroom” was no longer available.

McGovern-Fraser Commission Impact Analysis

Understanding how party-line voting, also known as party unity voting, changed is critical to understanding the impact of the 1972 McGovern-Fraser Commission candidate selection recommendation-based rules change. Our analysis considers:

  1. The legislative voting record for all legislation before and after the rules change.

  2. The difference of the direction and power of the party unity voting correlations before and after the rules change was implemented.

To this end, we analyze a dataset from the Brookings Institution. (4) The dataset aggregates party unity votes by indicating the percentage of all roll call votes on which a majority of voting Democrats opposed a majority of voting Republicans. We divided the dataset into two groups:

  1. a "PRE" group, which is all congressional votes from 1953 to 1972, and

  2. a "POST" group, which is all congressional votes from 1973 to 2016.

If the 1972 McGovern-Fraser Commission candidate selection recommendation-based rules impact lawmakers, we would expect a change in direction and power of the correlations between these 2 groups. In fact, our results demonstrate lawmaker impact.

In the PRE group, we noted almost a "gun shot" correlation, where unity voting is almost uncorrelated over time. Our analysis approach is based on a statistical regression that regresses the year of the legislative vote (x-axis) on the degree of party unity (% of unity) of that year's legislative voting (y-axis). If anything, the trend line shows a decline in unity voting from 1953 to 1972. The power of the correlation is shown as R^2. An R^2 of 1 is perfect correlation, an R^2 of 0 is no correlation. In this case, .13 (.33) means there is little correlation in the Senate (House), or only about 13% (33%) of the Senate (House) unity maybe explained by time.

The POST group shows a different story. The trend shows increasing party unity (or a decrease in bipartisanship) from 1973 to 2016. Also, the correlations are more powerful. While the House correlation is about the same (PRE=33% vs. POST= 36%), the Senate is over 3.5x more correlated. (PRE=13% vs. POST= 48%). Thus, in the Post 1972 McGovern-Fraser Commission candidate selection world, legislative voting is moving more toward party unity voting AND the strength of the correlations are higher.

To help show the power and direction of change before and after McGovern-Fraser, the next graphic shows The Big Pivot. This shows the PRE and POST change side-by-side comparison and the increasing party unity voting trend since 1972.

As the reasoning truism suggests, "correlation is not necessarily causation." As such, this analysis may not entirely demonstrate the McGovern-Fraser Commission recommendation "caused" increased party unity. As far as I know, there is no comparable parallel universe control group where McGovern-Fraser did not exist. However, certainly "correlation and causation may exist at the same time" so an increasing correlation and the intuitively affirming direction of the correlation provides some weight of evidence.

Since the correlations in the POST world are between 30% and 50%, there are additional factors at play driving partisanship. This is not surprising, given the messy, dynamic world of politics. However, our analysis shows the McGovern-Fraser Commission recommendation-based rules change is likely part of the evidence underlying legislative partisanship and leading to a weakening of our vote. In our article, Preventing the 2021 U.S. Capitol attack, we examine underlying vote weakening causes, including consistency with game theoretical stable solution outcomes. We also consider vote strengthening initiatives, including changes that encourage our legislators to “promote general welfare” of U.S. citizens. (5)


(1) GovTrack Senate and GovTrack House, Civil Rights Act of 1964, United States Government

(2) Social Security Legislative History, Social Security Administration, United States Government

(3) Obamacare Overview, Ballotpedia, an encyclopedia of American politics

(4) Vital Statistics on Congress, Chapter 8, 8-3 Party Unity Votes in Congress, 1953 - 2016 (percentage of all votes)

(5) “Promote general welfare” is one of the stated objectives of the U.S. Constitution.

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