Amid the hothouse atmosphere that has developed in Washington in recent days, some are seeing a strategy emerging from President Trump’s increasingly frequent and brazen broadsides against his opponents in the impeachment debate.

At this point, the strategy goes, Mr. Trump might as well urge House Democrats to bring on an impeachment case. That seems likely to happen anyway, so get your core supporters as agitated as possible in preparation. The impeachment case then would move to the Senate, controlled by fellow Republicans,...