Which brings us to the final wall. The strongest arguments against removing Trump fall under the heading of prudence. They hold that while he abused his power, it would be better to let voters judge that abuse in the upcoming election than for Congress to remove him; that his removal would be bitterly divisive; that it would set a dangerous precedent, encouraging Congress to strike against presidents over trivial disagreements. Like a nuclear weapon, in short, impeachment should be deployed extremely sparingly if at all.

The analogy is common but inapt. It is a nuclear weapon that replaces the president with his own handpicked ally, making it less potentially devastating in that respect than a general election. It also can’t be deployed unless the public has a much larger level of support for it than it has mustered for any presidential candidate in decades. Only once in U.S. history has a president left office because Congress was going to remove him. The possibility of impeachment is a weak check on the presidency and cannot be made into a strong one.

It might be possible to regard Trump’s Ukraine misadventure as a lapse of judgment, with little harm done, if he showed any repentance or even understanding of what he has done wrong. Instead it looks more like a window into tendencies of his that are incompatible with performing the functions of his office.