Susan Davis reports on the presidential race.

Liberal advocacy group MoveOn.org will begin airing a new ad nationwide and in Arizona starting Tuesday that links expected Republican nominee John McCain to President Bush.

The ad aims for the funny bone, showing goofy images of McCain and Bush set to the lyrics of the “Patty Duke Show.” (Still they’re cousins/ Identical cousins and you’ll find/ They laugh alike, they walk alike/ At times they even talk alike.)

Broader Democratic efforts to link the Arizona senator to the unpopular president are not new—the campaign of Democratic front-runner Barack Obama criticized the “Bush-McCain” foreign policy agenda in a speech last week—and that strategy will likely intensify in the general election campaign.

MoveOn’s ad will be airing nationally on CNN and in Arizona markets to coincide with a Tuesday fundraiser featuring McCain and Bush in Phoenix. The McCain campaign, as reported in today’s Wall Street Journal, has made a concerted effort to maintain distance from the Bush administration with the president’s favorability rating at a record low. It is the first time the two men will appear together in nearly three months.

The ad is also featured on a Web site called the “Bush-McCain Challenge” modeled off the old “Pepsi-Coke Challenge” ad campaign. The site, paid for by MoveOn, asks visitors to guess whether McCain or Bush has made certain statements about the Iraq War, abortion, guns, among others. According to MoveOn, half a million people have taken the on-line challenge.

UPDATE: “Today, John McCain released a serious ad outlining his vision for the future of the nation. Contrast that to Barack Obama’s supporters, who issued a ridiculous ad that is backward looking and belittles the seriousness of this election,” said Republican National Committee spokesman Alex Conant in a statement. “It’s clear MoveOn.org does not want this election to be about who has the experience and judgment necessary to lead us into the future.”