Who is More Liberal, Senator Obama or Senator Clinton?

by Royce Carroll, Jeff Lewis, James Lo, Nolan McCarty, Keith Poole, and Howard Rosenthal

Senator Obama is at most marginally more liberal than Senator Clinton but the difference is negligible. The two are essentially identical ideologically based upon our DW-NOMINATE scores estimated from all roll call votes cast in Congresses 1 – 110 (through the 1st Session of the 110th, 2007). (The House and Senate were scaled together simultaneously using the 630 members who served in both Chambers.) Clinton and Obama have served together since 2005 (Obama was elected to the Senate in 2004 and Clinton was elected to the Senate in 2000, so they have only overlapped for 3 years).

The two are by no means the most liberal Democrats in Congress. There are a total of 286 Democrats in the 110th House and Senate (counting replacements). There are 88 members to Obama’s left — 8 Senators and 80 Representatives. The 8 Senators are Feingold (D-WI), Whitehouse (D-RI), Sanders (I-VT), Boxer (D-CA), Kennedy (D-MA), Brown (D-OH), Lautenberg (D-NJ), and Levin (D-MI). Between Obama and Clinton are 8 members — one Senator, Akaka (D-HI) — and 7 Represenatives. To Clinton’s right there are 188 Democrats — 40 Senators and 148 Representatives. There is no overlap of the two political parties. They are completely separated ideologically.

In the 110th Congress the first dimension DW-NOMINATE scores for Democrats range from -0.771 (Lee D-CA-9) to 0.015 (Taylor D-MS-4) with a mean of -0.370. The Republican mean was 0.473.

The smoothed histogram below shows the distributions for both political parties in the 110th (2007) House and Senate. The smoothed histograms give a more accurate perspective about the relative liberalness of Senators Clinton and Obama. In particular, Senator Obama is located at -0.436 and Senator Clinton at -0.427, placing them just to the left of the average Democrat. Senator John McCain and President George W. Bush are shown on the Republican side (President Bush can be placed on the dimension using Congressional Quarterly Presidential Support roll calls).

Combining the two Chambers shows even more clearly the fact that Senators Clinton and Obama are essentially identical ideologically with a substantial number of Democrats to their left. Senator McCain is in the left wing of the Republican Party and President Bush is on the conservative edge of his Party.

Below is an enlargement of the Democratic Party showing a variety of important Democrats over the past 20 years. The late Senator Wellstone (D-MN) was the most liberal Senator since the end of World War II. His position is just to the left of Senator Feingold (D-WI). Former Senator Nunn (D-GA) was a highly influential moderate during his period of service in the Senate. Senator Kennedy (D-MA) is just to the left of Speaker Pelosi (D-CA). Finally, Senator Lieberman (D-CT) is relatively moderate based upon his voting with the Republicans on national security and Iraq-related issues.

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