Chuck Hagel is the most disputed nominee for defense secretary since the first President Bush sent up John Tower’s name in 1989. Tower was rejected by the Senate, but his foes were Democrats. Yet Hagel’s primary critics are Republicans, Hagel’s party during his dozen years in the Senate. An examination of his tenure on Capitol Hill shows that Hagel’s alienation from the GOP stems from votes against party initiatives, hostile rhetoric against the Bush White House and criticisms of his congressional colleagues.

In the Senate, Hagel was rigorously conservative on domestic policy, with a voting record rated 84 percent by the American Conservative Union. Exclusively on foreign-policy matters were Republicans riled. Rows began early. Hagel was one of the few Republicans to advocate sending ground troops to Kosovo in 1999, co-sponsoring a failed resolution. (He was supported by his current nemesis John McCain.) Fully 187 Republicans opposed the plan. Who was Hagel’s main opponent? Oklahoman Republican Senator James Inhofe. “[T]his is just depleting and diluting our resources,” said Inhofe at the time. “We should not be in Kosovo.” Ominously for Hagel, Inhofe is now the ranking member of the Senate Armed Services Committee and among the most influential senators who could vote against Hagel’s confirmation.

With the exception of Kosovo, Hagel was often indistinct from the majority in the Republican caucus. He voted in favor of the war in Afghanistan, developing a missile defense program, increasing defense spending, maintaining the “Don’t Ask, Don’t Tell” policy on gay soldiers, reauthorizing the Patriot Act and opposing the Comprehensive Nuclear Test-Ban Treaty. He voted for the Iraq War.

Few legislative dissensions actually occurred, but they all became high-profile matters. In mid-2007, Hagel joined only two other Republicans in supporting Democratic-sponsored legislation mandating swift withdrawal from Iraq. That same year, Hagel opposed Bush’s surge in Iraq, which turned out to be his most fateful vote. In response, Dick Cheney said he believed “in Ronald Reagan’s 11th commandment: thou shalt not speak ill of a fellow Republican. But it’s very hard sometimes to adhere to that where Chuck Hagel is involved.” Finally, Hagel once voted against imposing sanctions on Iran, though on another occasion he voted for them.

Thus, there were only three important votes on which Hagel abandoned his Republican colleagues. More lasting in their memory, perhaps, were his frequent, unbridled criticisms of the Bush White House and the Republican Party in general. He criticized Bush’s “Axis of Evil” speech, and said Iran was helpful to the United States in Afghanistan. He also challenged early calls by McCain and Senator Lindsey Graham for war with Iraq, contending that there was “absolutely no evidence” of Saddam Hussein’s continued nuclear weapons program. A week before the invasion, he insisted that “the diplomatic channels have not yet been fully exhausted.” Hagel suggested that the United States should instead try to improve relations with the countries Bush had branded an "axis of evil"—Iraq, Iran and North Korea. The Weekly Standard countered that he had become a member of the "axis of appeasement."

Despite voting to invade Iraq, Hagel was always unenthusiastic: “[W]e do not really know if our intervention in Iraq will lead to democracy in either Iraq or elsewhere in the Arab world,” he said in 2003. Hagel also criticized Bush’s Guantanamo Bay policies—even as he voted against restoring civil liberties to detainees in the prison.

After the Iraq insurgency sprouted, Hagel became arguably the highest-profile Republican opposition figure. In 2004, he called the situation in Iraq “beyond pitiful.” Senator John Kerry, who challenged Bush in 2004, quoted Hagel’s comment during his campaign, maddening Republicans.

Bush’s second term saw Hagel breaking even more dramatically with his party on foreign-affairs issues, at least in his public remarks. He mocked Cheney’s comments that the insurgency was in its last throes. He condemned Defense Secretary Donald Rumsfeld, and said “nothing surprised” him about the incompetence of the administration. He even twice suggested Bush’s impeachment. While many Republicans sought to distance themselves from the Bush administration, no one else lambasted it so openly and starkly.

In 2006, Hagel said that the “Jewish lobby intimidates” Congress, and that he was an American senator, not an Israeli senator—a choice of words that would come back to haunt him. He pushed for direct negotiations between Israel and Hamas and between the U.S. and Hezbollah, and publicly sympathized with the Palestinians. Remarks like these—though rarely buttressed by corresponding legislative actions—are among his most contentious.

In personal terms, the fallout has been extremely costly. McCain, once a friend, now raises serious doubts about his former colleague’s fitness for the nomination. By all accounts, Hagel’s opposition to the Iraq surge sealed this falling out. “[T]he split began over the length and cost of the Iraq war and Hagel’s decision to not support the surge, which John took as a personal insult,” a McCain friend told a reporter. Compounding the breakup was Hagel’s decision to withhold a McCain endorsement in the Republican primary. The Nebraska senator also criticized his colleague by name. McCain “thinks we just need more military,” Hagel said at the time. “I’ve talked to John about this many times. I’ve said, ‘John, we’re limited. We’re doing tremendous damage to our Army and Marines, we can’t sustain this.’” He said McCain’s repeated calls for Russia to be expelled from the G8, the association of major industrial democracies, were “completely crazy!”

Symbolizing the separation, Hagel skipped the 2008 Republican convention. He was perhaps the only senior Republican elected official who publicly criticized McCain’s choice of Alaska Governor Sarah Palin as his running mate. He declared, “There is no question that this candidate is arguably the thinnest-résumé candidate for Vice-President in the history of America.”

Hagel said he was “very disappointed” by McCain’s campaign overall. “He gave one unifying speech and then has spent fifty million dollars to destroy his opponent.” He broadened his critique to encompass all Republicans. “There was a political party in this country called the Know-Nothings,” he continued. “And we’re getting on the fringe of that, with these one-issue voters—pro-choice or pro-life. Important issue, I know that.”

Over the course of a decade, his evolving views on foreign-policy matters estranged Chuck Hagel from his former Republican friends. At least one lesson can be gleaned from today’s controversy over his confirmation: One’s choice of words and maintenance of relationships matter—every bit as much as one’s legislative record.

Jordan Michael Smith, a contributing writer at Salon, has written for the New York Times, Washington Post, and Boston Globe.