Liberals and Democrats often say John McCain is just running for George W. Bush's third term as president. Apparently, McCain has had enough of that particular accusation, because he unveiled a new retort to it in an interview with NBC's Brian Williams that aired Monday night.

"Senator Obama says that I’m running for a Bush's third terms [sic]," McCain said, according to a transcript of the interview. "It seems to me he's running for Jimmy Carter's second."

It's a pretty cute response -- I laughed a little, I'll admit -- but its political value seems minimal.

Given Bush's historic unpopularity, the linkage between Bush and McCain is quite damaging for the presumptive Republican nominee. Moreover, Bush's presidency is fresh in voters' minds. On the other hand, Carter lost his bid for reelection to the presidency in 1980. That means anyone who was old enough to vote for or against him will be 46 or older by the time this election rolls around. According to exit polls from 2004, at least 46 percent of the people who voted for president last time around were younger than that. That's a whole lot of people who might not get the joke as fully as McCain would like.