I don’t get it. Why wouldn’t a first-term Democratic incumbent up for reelection in an increasingly red state want a photo op with the Unicorn Prince?

Claire McCaskill will not be attending the Democratic National Convention in Charlotte, a McCaskill aide confirmed to TPM Tuesday. McCaskill joins a list of vulnerable Democratic politicians whose home districts are hostile ground for President Obama and who will be steering clear of the convention.

“In years when Claire is on the ballot, she has historically not gone to the convention,” the aide said, “because she believes it’s important to stay in Missouri to talk to voters.”

Turns out she didn’t go to the convention in 2004 either when she was running for governor, but c’mon. McCaskill’s no ordinary Democrat when it comes to Obama: She was among the first senators to endorse him over presumptive nominee Hillary Clinton in 2008, doing so just five days after Hillary’s big win in New Hampshire. That was a major vote of confidence in him coming from a key swing-state senator and prominent woman pol; Team Clinton “aggressively sought” her endorsement at the time but McCaskill stuck with Hopenchange. As recently as last October, notes National Journal, she was defiant in standing by her buddy O:

Sen. Claire McCaskill, D-Mo., makes clear to the St. Louis Beacon that she won’t be running and hiding from President Obama, even as she faces a tough reelection bid in a state the president’s almost certainly not going to win.

McCaskill said she will be asking Obama to stump for her and help her raise money, but added that she doesn’t always agree with him.

Vulnerable Democrats in comparable positions should take notice. Opponents will tie McCaskill to Obama no matter what she does: She was a major surrogate in 2008 and there are plenty of photos of the two for TV ads (Republican John Brunner has already run one tying the two together). Running away from Obama will only generate negative press coverage (when McCaskill missed an early October Obama fundraiser, that was a story).

Eight months later, here she is running away. I wonder what finally convinced her. Was it his gay marriage “evolution”? She conspicuously refused to join him in endorsing SSM last month, preferring a federalist punt instead. Maybe it was the terrible May jobs report and the prospect of no relief in sight? Or was it his new amnesty-by-fiat DREAM policy? Or was it the cumulative effect, leading to a dim awareness on her part that the words “Obama” and “good news” haven’t appeared together in a sentence in years?

Exit question: How many convention cancellations does this make? McCaskill, Manchin, Tester, Matheson, Tomblin, Rahall, Critz — who else? Good lord. No wonder they’re moving to a smaller venue. At this rate, Obama, Biden, and OWS will be the only ones there.

Update: Dan McLaughlin: “If this many in his party were bailing on attending the convention of an incumbent GOP POTUS, media would spin it as sign of his extremism.”