Republican maverick John McCain (search) campaigns with President Bush. He's good friends with Democrat John Kerry (search). And, in an unusual twist, he's shown up in campaign advertisements for both.

The Arizona senator is a hot commodity as Republicans and Democrats alike seek to capitalize on his popularity among people of varying political persuasions, especially independents who both campaigns are working overtime to reach this year.

It's rare that a politician has appeared in ads that praise two competing presidential candidates.

"It's clearly uncommon," said Bill Benoit, who studversity of Missouri-Columbia.

McCain faced Bush in a bitter Republican primary four years ago but has endorsed the president this year. He will be the featured speaker Monday night, opening the Republican National Convention in New York.

A Navy bomber pilot who was a prisoner of war in Vietnam for more than five years, McCain became friends with Kerry while the two worked closely together to end the trade embargo against Vietnam and establish diplomatic relations with the country.

It's clear why both sides see McCain as an asset. Polls show that by almost a 3-to-1 margin, Americans have a favorable view of the GOP senator and he appeals to moderates and liberal Republicans, which both campaigns are courting.

Once considered by Kerry as a possible running mate, McCain was featured in a Bush ad that was rolled out just as Kerry announced John Edwards as his running mate in July.

The ad suggested that McCain was Kerry's first choice for a No. 2 spot on a bipartisan ticket. It showed McCain at a campaign event with Bush, praising the president for leading with "great moral clarity and firm resolve."

In May, Kerry's campaign used the Republican in a biographical ad meant to attract independents and anti-Bush Republicans and to show that the Democrat could work with people on both sides of the aisle.

"He joined with John McCain to find the truth about POWs and MIAs in Vietnam," the Democratic ad said of Kerry. It showed Kerry with his hand on McCain's shoulder.

Unlike with Bush, McCain did not bless Kerry's use of him in ads. However, he did not dispute it either — at least until last week.

Responding to a Republican-fueled controversy about Kerry's own decorated Vietnam war record, Kerry's campaign rolled out one ad condemning the attacks and referencing McCain's primary bid four years ago in which Republicans attacked the former prisoner of war's patriotism. The ad said: "Bush smeared John McCain four years ago. Now he's doing it to John Kerry."

Another Kerry ad showed a clip of McCain telling Bush at a debate in February 2000 that Bush "really went over the line" by refusing to denounce "a fringe veterans group" that had accused McCain of abandoning veterans. "You should be ashamed," McCain says.

A day after that ad's release, McCain called on Kerry to stop using the footage. Kerry's campaign complied, pulling the ad from the airwaves.