John McCain and Chuck Hagel were once BFFs. What happened?

John McCain and Chuck Hagel, best friends no longer.

We’re talking about John McCain here, so anything could have happened to set him off…

The Washington Post – Chris Cillizza

When Chuck Hagel sits before the Senate Armed Services Committee, one face staring back at him will be decidedly familiar — that of Arizona Sen. John McCain.

McCain, the ranking Minority member on Armed Services, and Hagel were once inseparable — two decorated Vietnam veterans who found common-cause in rebelling against their own party orthodoxy. McCain campaigned for Hagel in the latter’s first race back in 1996 – here’s visual evidence — and Hagel was one of four Senators to endorse McCain’s 2000 presidential bid. The duo even had Senate offices close to one another to stay in constant touch.

Now, the two mens’ friendship has, by most accounts, dissolved entirely. McCain, in a statement shortly after Hagel’s nomination as Secretary of Defense was made official Monday, said that he has “serious concerns about positions Senator Hagel has taken on a range of critical national security issues in recent years.”

So, what happened? And why?

The answer, as you might suspect, isn’t a simple one. One Republican familiar with the two men insisted there was “no blow up or argument really” and that Hagel simply “stopped coming by the office or socializing outside the Senate.” In conversations with a number of people familiar with the relationship, however, it’s clear that a combination of policy disagreements, political slights and personality conflicts led to the collapse of a once-close friendship.

The most obvious break in the McCain-Hagel relationship came in the early 2000s over the war in Iraq. While Hagel, like McCain, voted for the use of force resolution against Iraq, he was always wary of America going it alone in the conflict and, as time wore on, became a more and more outspoken critic of the war.

McCain, on the other hand, remained a stalwart defender of the necessity of the war and went on later in the decade to become the face of the surge strategy to put more troops in the country. Hagel opposed that strategy and panned it repeatedly.

“Quite simply, the 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,” said one McCain ally granted anonymity to speak candidly about the relationship. “It’s very sad.”

While a disagreement over the right course of action in Iraq might have been the biggest factor in the dissolution of the friendship, politics also played a role in the split.

While Hagel was intimately involved in McCain’s 2000 presidential bid — he served as national co-chairman and was in New Hampshire the night the Arizona Senator won the Granite State presidential primary — by the time McCain ran for president again in 2008 Hagel was much less on board.

Not only did he not endorse McCain, but Hagel also didn’t entirely dismiss the idea of serving as then Sen. Barack Obama’s vice presidential nominee. (Hagel’s wife endorsed Obama in the 2008 race.)

Then, in 2012, Hagel endorsed the candidacy of former Nebraska Sen. Bob Kerrey (D) in the Cornhusker State’s open seat Senate race, a move that badly rankled McCain, who had endorsed Kerrey’s opponent — Republican Deb Fischer — and campaigned with her the day after Hagel made his endorsement of Kerrey public.

Adding to their policy and political disagreements, there was (and is) the fact that McCain and Hagel are similar enough in terms of their personalities — hard charging, irascible, certain that their deeply-held beliefs are correct — that they were always destined to be either best friends or the exact opposite. Put simply: The very personality traits that made McCain and Hagel fast friends in the mid 1990s is what has driven them apart in the last few years.

While no one disputes that the once-close relationship is in tatters, one source familiar with the two men voiced hope that the break is temporary, not permanent. ”It’s like brothers who get in a big fight and don’t talk for a while.” said the source. “They’re still brothers.”

Maybe. How McCain treats Hagel during the confirmation process will be a telling indicator of whether a reconciliation is in the offing or whether the relationship has been irreparably damaged.