Party politics may be important, “but it’s not more important than what’s good for the country.” That’s what Joe Lieberman said Monday, as he crossed party lines and endorsed Republican John McCain for President.

Lieberman was the Democratic vice-presidentical candidate in 2000, and now calls himself an Independent Democrat. So why isn’t he backing a Democratic candidate? The Connecticut Senator says none of them asked for his support. Besides, he thinks the Party has abandoned a tradition of strong defense policy.

So when his long-time friend John McCain came calling, Lieberman decided he’d support a Republican this time around. Both are hawkish on the war, they’ve traveled the world together, and they’ve worked together on major issues like climate change and establishing the 9/11 commission. McCain calls his colleague “courageous” for backing him regardless of the consequences.

Indeed, the endorsement is not sitting well with some leading Democrats. But Lieberman shrugs it off, saying Democrats probably view him as an “eccentric uncle.”

Could Lieberman show up as a vice-presidential candidate again? This time on the Republican ticket? Lieberman insists he’s happy as a Senator. But McCain says if he’s elected, his old friend would continue to be an advisor, and would certainly play a role in a McCain presidency.