On Monday, President Trump was already having a bad week.

The coronavirus was spreading, the stock market was plummeting and his administration was getting blamed for an inadequate response to a health crisis.

Then came Tuesday. Joseph R. Biden Jr., whom Mr. Trump was so eager to paint as corrupt that his attempts to do so led to his impeachment, pulled off one of the most remarkable political comebacks in recent history, winning nine states and joining Senator Bernie Sanders as a front-runner in the Democratic presidential race.

U.S. stocks did make a comeback on Wednesday, closing nearly 1,200 points up, which counted as good news for a president betting the farm on a healthy economy. The bad news was the reason many analysts cited for the gains was Mr. Biden’s Super Tuesday victories.

For Mr. Trump, whose belief in his own ability to shape external events is a source of comfort, it has been a week of confronting the fact that almost nothing is in his control right now.