Likewise, what’s politically unthinkable today may become fact in a few years. If it seems impossible to you that presidential power could be any more heinously abused than it has already been—well, that’s just a failure of imagination. The primary goal of impeachment should be to prevent even more serious presidential malversation in the future.

With that goal in mind, Congress should signal as strongly as possible that President Trump’s Ukraine scheme is unacceptable. But given the heightened partisanship in both chambers, it seems certain that the full House vote on impeachment and the Senate vote in the subsequent impeachment trial will be almost entirely along party lines. The best scenario within the realm of plausibility would involve a (slightly) bipartisan majority of senators voting to convict President Trump, even if the number falls short of the two-thirds supermajority required for his removal.

But even this outcome would have real value. It would establish that the present scandal is broadly unacceptable behavior. Seeing that the Ukraine scandal escalated from initial reports to impeachment within four months would make a future president think twice about emulating the Trump administration.