HILLSBOROUGH, N.H. -- Sen. John McCain, trying to keep momentum in this state's critical Republican primary race, brought in something unusual on Monday -- an endorsement from the other party.

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Sen. Joseph Lieberman, the Democrats' 2000 vice presidential nominee, said he was intending to wait until after the primaries to make a choice for the 2008 presidential race. But McCain asked for his support and no Democrat did.

Lieberman, an independent who caucuses with the Democrats, said he chose his longtime Senate colleague because he has the best shot of breaking partisan gridlock in Washington. Both men also support the war in Iraq.

"On all the issues, you're never going to do anything about them unless you have a leader who can break through the partisan gridlock," Lieberman said. "The status quo in Washington is not working."

Independents can vote in New Hampshire's first-in-the-nation primary on Jan. 8 and they are the people McCain is targeting, much as he did in winning the state's Republican primary in 2000 over George W. Bush.

Traveling with Lieberman Monday, McCain said the Connecticut senator is his answer to the people he hears in every town hall meeting who ask, "Why can't you all work together?"

For McCain, behind in the polls here but gaining, the endorsement carries the risk of alienating conservatives who have been critical of his support for immigration and campaign finance reforms.

"If I get some criticism for aligning myself with a good friend I have worked with for many years, I will be more than happy to accept that criticism," McCain said.

For Lieberman, it marks another turn away from his party.

"Political party is important, but it's not more important than what's good for the country and it's not more important than friendship," Lieberman said.

Lieberman won re-election to the Senate in 2006 as an independent, after losing the Democratic primary largely because of his support for the war. High-profile Democrats abandoned him after the primary defeat.