Nobody doubts a Democratic House can produce 218 votes for impeachment. It probably doesn’t matter much what the charges are. In some sense, that’s where impeachment should land: The charges matter less than whether, under the totality of considerations, a president should be removed before his term ends.

Democrats are still living down previous quotes about the need for a broadly supported impeachment. Nancy Pelosi, for one, likely regarded herself as handcuffed by the Ukraine whistleblower. If Mr. Trump were re-elected and she had failed to pursue impeachment, a freight train of blame would have come her way from her own caucus. Her chances of being re-elected speaker would be nil.

Here’s guessing this is how we really got today’s partisan impeachment. There is still a chance, of course, that the charges themselves could alter the equation, by shifting opinion in the body politic. Can the Ukraine charges do it? No and yes—but Democrats are pushing bad assumptions that voters would be advised to think twice about:

That Ukraine is our dear ally, in whose conflict with Russia we should become deeply engaged.

That politics stops at the water’s edge. (It never did.)