Yet the Democrats may end up paying a higher political price than they anticipate. The trial won’t only delay Mr. Biden’s program. It will tarnish his image as a “unifier” eager to work across party lines. That identity will be much harder to sustain after Democratic senators vote in lockstep to convict Mr. Trump and push through a mammoth Covid relief bill without any Republican votes.

With all or almost all Democrats supporting Mr. Trump’s conviction, the president will be pressed to declare his position. Whether Mr. Biden speaks out or not, he signaled his position when he refused to dissuade Mrs. Pelosi from transmitting the House’s article of impeachment to the Senate. The speaker wouldn’t have done so over the new president’s opposition.