This week’s renewed enthusiasm for impeachment would be a great deal more persuasive if it were not No. 6,782 in a series. Democrats want to impeach Trump for leaning on the Ukrainians about the Biden’s family’s shady dealings — and they are shady — with that corrupt regime and its sycophants. Before that, they wanted to impeach Trump because favor-seekers book rooms in hotels with his name on them. Before that, they wanted to impeach him because of his Twitter habits. Etc.

The cynic in me guesses that the Ukrainian gambit serves a dual purpose: First: It provides a pretext for a pre-election impeachment inquiry against the incumbent president — which, given the current composition of the Senate, is unlikely to end in action before the election, or after that, either, unless there is a Democratic majority seated in the Senate. Second: The likely collateral damage to Joe Biden probably is not entirely unwelcome in some Democratic circles — he already is sliding vis-à-vis Senator Warren, and to many Democrats he already has the look of a likely loser should he be the nominee. If somebody has to be put on an ice floe, it’s going to be Joe Biden.

There are many problems with this approach, one of which is this: Americans in possession of even a modest political memory must recall that not only did Democrats insist that the 2016 election was illegitimate, they also insisted that the last election that brought a Republican to the White House was illegitimate. There was talk of impeaching George W. Bush, too — talk that was endorsed by, among others, Donald Trump, who was a donor to Mrs. Clinton’s campaigns before he became her tormentor. For the Democrats, there is only one kind of legitimate presidential election: one where they win.