Ideological Makeup of the Parties: 1920, 1970, and 2020

I have completed my MC-Index for the 116th Congress, with 43 votes being counted towards a conservative score in each chamber. I’ll be posting details after the Amy Coney Barrett vote, and I am counting the vote currently based on what senators have said, and given this, only Susan Collins will among Republicans be voting against her while all Democrats are expected to vote no. I have counted score for the Senate thusly. Based on averages of my data for the chambers in each of these sessions, I have calculated the following for 100 years ago, 50 years ago, and now. These are not life scores for the named politicians, just what they scored in the session:

66th Congress (1919-21)


Republican Representatives: 80%

Democratic Representatives: 19%

Lowest Republican: James H. Sinclair, N.D. – 29%

Highest Democrat: William Kettner, Calif. – 100%


Republican Senators: 80%

Democratic Senators: 20%

Lowest Republican: Charles L. McNary, Ore. – 42%

Highest Democrat: James K. Shields, Tenn. – 82%

91st Congress (1969-71)


Republican Senators: 63%

Democratic Senators: 30%

Lowest Republican Senator: Clifford P. Case, N.J. – 2%

Highest Democrat: Richard B. Russell, Ga. – 90%


Republican Representatives: 72%

Democratic Representatives: 34%

Lowest Republican: Ogden R. Reid, N.Y. – 8%

Highest Democrat: William M. Colmer, Miss. – 100%

116th Congress (2019-21)


Republican Senators: 84%

Democratic Senators: 6%

Lowest Republican: Susan Collins, Me. – 37%

Highest Democrat: Joe Manchin, W.V. – 38%


Republican Representatives: 85%

Democratic Representatives: 5%

Lowest Republican: Brian Fitzpatrick, Penn. – 24%

Highest Democrat: Ben McAdams, Utah – 42%

Explanation of Data

There may be some things that stood out to you. For one, the Senate Republicans are 21 points more conservative on average in 2020 than they were in 1970, and House Republicans are 13 points more conservative. This coincides with the descent into irrelevancy of the Rockefeller Republicans, who were stronger in the Senate than the House and could be much more liberal than the so-called “RINOs” of today. The Senate Democrats are 24 points more liberal on average in 2020 than they were in 1970, demonstrating the McGovern wing’s success at taking over the Democratic Party. The Republicans are far closer to what they were ideologically in 1920, when in both chambers their members averaged an 80% for the 66th Congress. Wilson fatigue was at its peak and the GOP had an election blowout that ushered in the conservative Harding Administration (Warren Harding was, as a senator, nearly as conservative as Barry Goldwater). Notably, in the Senate, I counted six votes regarding the Versailles Treaty, the most important issue to come before that Congress. One hundred years later, the Republicans are four points higher in the Senate and five points higher in the House.

The notion that Democrats were more conservative in 1970 than in 1920 may surprise people, but there is an explanation: Southern Democrats had by 1970 grown quite conservative, while fifty years before they were usually supporters of the Wilsonian brand of liberalism. Northern Democrats, on the other hand, had grown considerably more liberal thanks to the influence of FDR. The last Northern Democratic president before Wilson was Grover Cleveland of New York, who had proved too conservative for his own party by 1896.

The Democrats in general may be higher in their liberalism in this Congress given opposition to President Trump, but the party has grown more liberal in the past twenty years. The Republicans too have grown more conservative in the past twenty years as there were more moderates in both chambers at the time.

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