The Poole reports on voting records in Congress provide one of the clearest analyses of relative position in voting records between members. Now the author of the Poole reports, Keith Poole of UC San Diego, has partnered with a number of his colleagues to analyze the relative position of the three Presidential candidates with their parties and on the general political spectrum. Poole et al determine that Barack Obama and Hillary Clinton occupy almost the same spot on the spectrum, well within the liberal mainstream of the Democratic Party — and John McCain’s reputation as a maverick is well earned:

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 — see our Technical Issues page for all the information about estimation issues and how the graphs below were constructed.) Clinton and Obama have served together since 2005…

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). … Senator McCain is in the left wing of the Republican Party and President Bush is on the conservative edge of his Party.

The data here goes much more in depth than the National Journal reports that pegged Obama as the most liberal Senator in 2007. The actual Poole report for that year shows Obama at 11th place, still significantly out to the Left of the median. Russ Feingold wins the #1 slot for Most Liberal, and Poole shows that Feingold is a consistent outlier in the Democratic Party. To no one’s great shock, Paul Wellstone was the biggest Leftist in the Senate since World War II until his tragic demise in 2002, and Feingold replaced him afterwards. Hillary comes in 20th for 2007.

McCain comes closer to the middle of the spectrum than either Hillary or Obama. In fact, this looks very similar to the views held by the Pew poll sample released yesterday. McCain has split from his party more than either Democrat, and while still conservative, is much more moderate than his opponents. In looking at historic party trends, however, Hillary and Obama would have been considered solid liberals and party voters at any time over the last 40 years, while McCain’s position moved from the solid center of the GOP to the moderate side because of the party movement to the Right. In 1988, McCai’s position was at the dead center of the Republicans in Congress.

One other interesting point: the parties have removed almost all of the overlap between them. The Democrats have become purely liberal, and the Republicans purely conservative. The partisan divide is much more about real ideology and philosophy than about electoral politics, which is why politics has become so passionate. Among the three candidates running for President, only one of them has a track record of working to fix that — and it’s not Barack Obama.

Be sure to read all of Poole’s analysis. Bottom line: both Obama and Clinton represent the mainstream liberal position of their party and have little evidence to show that they would work towards compromise or bipartisanship. McCain comes closest to the center, and therefore covers much more political ground with the American electorate than either Democrat.