A year ago, the political world’s attention was fixed on the Oct. 13 meeting of the Penobscot Bay Regional Chamber of Commerce in Rockport, where Maine Sen. Susan Collins was finally going to say if she planned to run for governor in 2018.

When Collins announced that she would skip the race and stay in the Senate, the pundits were unanimous.

“This will be bad news for Donald Trump,” veteran political analyst Stuart Rothenberg told The New York Times. But he added that it would be good news for those in Washington “who are looking for dispassionate, pragmatic leadership and for members willing to cross party lines on important votes.”

A year and a day later, it’s almost impossible to remember what he was talking about.

In 2017, Collins was getting spontaneous applause in the airport on her way home from Washington; now she and her staff push past protesters to get to work. Back then, she was one of the most popular members of the U.S. Senate, with appeal that crossed party lines; now she is reviled by many of the same Democratic-leaning independent women who had once supported her campaigns.

What happened? Simple.

Collins stopped opposing Trump on issues that matter to a large number of her constituents. She voted for a tax bill that threatened key safety net programs by exploding the deficit. She failed to deliver a promised health insurance market stabilization bill, which was needed to fix problems that the tax bill had created.

And the pro-choice senator from Maine provided the crucial 50th vote for anti-abortion rights Supreme Court Justice Brett Kavanaugh, rationalizing the allegations of sexual assault against him by saying his accuser must have been mistaken.

That’s what happened. The more interesting question is: Why?

At least in part, it’s what comes from hyperpolarized politics. There are no stand-alone issues anymore. Every position you take signifies your true tribe.

But I suspect it also has something to do with what she learned when she explored the governor’s race.

Throughout the summer of 2017, a consensus emerged that the only thing that could stand between Collins and the Blaine House was a Republican primary. Collins, it was said, had problems with “the base.”

Gov. LePage called her “dangerous” in a Wall Street Journal op-ed, adding that she was “more interested in preening for the cameras than in making real progress.”

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