McCain, in Congress for 26 years to Obama's four, has the longer record of producing bipartisan alliances on tough issues. He has bucked his party again and again to do just that — on immigration, federal judges and campaign finance, to name three on which he enraged many Republicans by defying the party position and working with Democrats. McCain-the-maverick has reverted to party orthodoxy on taxes and other issues this year, which will put him in a bind if elected: Would he stick with those new positions, or compromise with the Democratic Congress he'd likely be working with?
As McCain points out on the campaign trail, Obama has a much thinner record of bucking his own party. With the exception of tough fights for ethics reforms in the Illinois Senate and in Washington — where he angered Democratic colleagues by insisting on the disclosure of lobbyists who bundle campaign donations — Obama has rarely challenged party dogma on the sort of big, contentious issues he'd face as president. As a U.S. senator, he has taken liberal Democratic positions on most issues. Studies by Congressional Quarterly show Obama has voted with his party almost 97% of the time, vs. about 85% for McCain.
Where Obama has diverged, it has often been rhetorical and reactive: After securing the nomination, he expressed disagreement with a Supreme Court decision that struck down the death penalty in cases of child rape, and he approved a decision that overturned a strict gun control law in Washington, D.C. He has signaled support for a modified form of affirmative action (extending it to poorer whites and denying it to better-off African Americans), and he has supported a key Bush initiative that funnels federal dollars to faith-based groups.
Obama's bipartisan accomplishments in Washington have been on significant, but relatively non-controversial, efforts to secure nuclear weapons and establish a federal-spending database. What he lacks is a record of challenging his own party on divisive, difficult issues — the deficit, immigration, energy — that he'd have to reach out to Republicans on if he's elected. Even with a Democratic majority in Congress, it takes 60 votes in the Senate to pass most major measures.