Biden fired the general counsel of the National Labor Relations Board, a Donald Trump appointee. America Rising, the Republican opposition research firm, began trashing Biden’s Cabinet picks. And on Thursday — one day after Biden urged the nation to “start afresh” — Mitch McConnell, the Senate Republican leader, was on the Senate floor accusing Biden of already taking “several big steps in the wrong direction.”

It all served as a bracing reminder of Biden’s arduous task ahead, and the obstacles in his path. The very structure of modern Washington, as Biden knows from his work in the Senate and as vice president, is built around the machinery of partisan war. Even in the absence of Trump’s polarizing presence, compromise remains anathema. And the best intentions and earnest rhetoric aren’t enough to alter that reality, even for a day.

“Every presidential inaugural is about unity,” said Matt Bennett of the center-left group Third Way. “But how do you do your presidential inauguration about unity at a moment when your predecessor tried to execute a coup two weeks before?”