With someone so close to Trump in the crosshairs, special counsel Robert S. Mueller III has every reason to examine any relationships between the Trump campaign and Russian officials or oligarchs in minute detail — and also to look closely at any Russia connections the Trump and Kushner family business empires might have.

The White House should thus be settling in for a long siege. The good news, from Trump’s point of view, is that his senior aides are discussing how to set up a “war room” to handle communications about the scandal, theoretically letting the rest of the administration get on with governing. The bad news is that Kushner has been involved in those discussions — when instead he should have been cleaning out his office.

Even setting the scandal aside, it is clear that Kushner gradually emerged as the most powerful of Trump’s senior advisers — and is not doing a very good job. His fingerprints were not on the health-care disaster; and while he hasn’t made relations between Israelis and Palestinians any better, he hasn’t made them any worse. But he has shown absolutely no sense of how to turn intention into legislation. And his instincts are so out of tune that he reportedly advised Trump that firing FBI Director James B. Comey would be a sure political win, rather than the equivalent of opening the gates of hell.