… What happened on Jan. 6 and the days leading up to it — an American president spending weeks trying to reverse the results of a free and fair election, culminating in his supporters storming the U.S. Capitol to try to keep him in power by force — was so shocking that it seemed at least possible (if unlikely) that it would break the pattern. Could Republicans stick with Trump again? And if they did, wouldn’t Democrats try to shame GOP senators as much as possible? …
In an alternate reality, Jan. 6 might have both strengthened the resolve of the party to dump Trump and also ease that break, since Republican lawmakers could argue that of course they were uncomfortable with a president whose supporters invaded the Capitol.
But the party’s base, particularly core activists, was overwhelmingly opposed to Trump being convicted in the Senate or facing any kind of punishment for Jan 6. Once that became clear, Republicans in Washington started citing an argument — one rejected by many legal experts — that it is unconstitutional to convict a president who is out of office. This was a convenient rationale — it allowed Senate Republicans to avoid both angering the base and defending Trump’s conduct in the run-up to and on Jan. 6. CONTINUED
Perry Bacon Jr., FiveThirtyEight