Mittens votes to convict
I am not terribly surprised that Mittens Romney voted to convict President Trump and remove him from office. His reasons for doing so are short-sighted, and he does not understand political reality.
From the moment Romney came to Washington as a Senator (having been endorsed by Trump in 2018) he wanted to establish himself as the "conscience" of the Republican Party, which is why he wrote an editorial in the Washington Post about Trump's bad character. Romney wants to be what John McCain was, getting praise and attention from the mainstream media. This vote was also about establishing a legacy.
Of course, Romney forgets that the same people praising him now were viciously attacking and smearing him in 2012 when he dared challenge the Great and Exalted Barack Obama. Romney would have faced the same treatment from 2013 to 2016 that Trump has faced from 2017 until now.
In addition to seeing himself as the conscience of the Senate, we cannot forget the role of a personality conflict here. Trump and Romney have been sniping at each other for years, and at least some of the reasoning for voting to convict was Romney's personal beef with Trump. The fact is that Trump (and his most toxic supporters) have caused a lot of personal rifts within the Republican Party, and a significant amount of the opposition to Trump within the Republican Party is fueled by that personal animus.
Would it be nice of people could put that aside and make decisions based only on logic, principle, and the law? Sure, but that is not how human beings work.
Now, does Romney legitimately believe that Trump is guilty of an abuse of power? I am sure he does, and his vote was in part one of principle. But we should not discount the role that his personal beef with Trump and his desire to cement a "statesmanlike" legacy have colored his perception of what Trump did. It is historically significant that the Republican nominee from 2012 voted to remove the Republican nominee from 2016 from office, but in the end, it will not really matter. This will not change a single vote in 2020.