By most measures, Senator Chuck Hagel (R-NE) doesn't seem a likely Republican to run for vice president on the Democratic ticket. A Reagan Republican through and through, he consistently receives high-marks from the NRA, opposes gay marriage, and supports drilling for oil in the arctic. So why do liberals consider Hagel the biggest fish in the pond of potential running mates? One word: Iraq.

Hagel is a Vietnam veteran who is considered one of Washington's most adept foreign policy minds. He vaulted to prominence this past year with his constant and brutal criticism of the war in Iraq. And while he begrudgingly supported giving Bush the authority to invade Iraq, Hagel was one of the first senators—Republican or Democrat—to declare the war a lost cause, calling the American strategy "dangerously irresponsible."

He has also provided bipartisan grist for the anti-war mill, most famously by telling Condoleezza Rice that sending more troops into Iraq was akin to sending meat into a grinder. Later, he advised colleagues who were waffling over their support of the war: "If you [want] a safe job, go sell shoes."

Those close to the senator say he is itching at the opportunity to join a ticket, either as a Democrat or with Michael Bloomberg as an Independent. "He's going through a period of introspection. He feels that the president and some of his own colleagues have flat-out deceived America about this war," says one insider close to Hagel. "He's always placed a premium on being straight with people—sometimes to the detriment of his own career—and what he's seeing now really upsets him."

While Iraq is certainly cause enough for Hagel to abandon the Republicans, his problems with GOP higher-ups have been brewing for some time. Hagel supposedly fumed over the Bush administration's slander of his friend John McCain in the South Carolina campaign, long after the election had passed. He also threatened to endorse Democratic Senator Max Cleland in 2002 after he discovered Bill Frist and the NRCC created ads linking Cleland—a triple amputee after Vietnam—to Bin Laden and Saddam Hussein. Says a Hagel ally, "Chuck is a conservative, but he puts an emphasis on fair play. He's never been about rhetoric and blind loyalty. He'll sign up in a minute with a Democrat if he feels like that person is the best choice for the country."