Washington (CNN) Republican Sen. Mitt Romney did something on Wednesday that he hadn't done in a quarter century in politics. By voting guilty on the first article of impeachment against President Donald Trump, Romney took a position that was wholly out of step with his party or his raw political self-interest.

It's true that Romney has been publicly critical of Trump since the 2016 election and only a nominal ally of the White House since entering the Senate last year. But in the years before Trump's takeover of the GOP, Romney operated less as a paragon of ideological principle and more as a political chameleon -- willing to be whatever he needs to be in any given moment.

His journey from a Massachusetts moderate to a conservative businessman to an elder statesman may have kept Romney afloat as a political figure, but it also contributed to his reputation as an inauthentic opportunist -- tacking in whatever direction he felt the party was headed.

With his guilty vote, that's no longer the case.

Once the definition of the Republican establishment, Romney is now, in the era of Trump, the one thing it was hard to imagine he'd ever be: a GOP maverick.

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