A Campaign That Started Slowly Gets Its Inevitable Upheaval

Remember a month ago?

This time in June, the presidential race was a dug-in contest between two elderly men who have already won presidential elections. The candidates were familiar. The polls barely moved. And if that (and my inbox) was any indication, the campaign felt to many voters like a dull trudge to the finish line.

So much for that.

Over the course of three and a half weeks in June and July, at a time when presidential campaigns are usually on cruise control before the conventions, American politics have been upended by three stunning turns that historians will parse for years to come: a disastrous debate for President Biden, the attempted assassination of former President Donald Trump, and now, the withdrawal of the incumbent just three and a half months before the election.

“I know it’s been a roller coaster,” Vice President Kamala Harris told her campaign staff on Monday, making something of an understatement.

When it comes to presidential campaigns, change often comes slowly and then all at once, with unscripted, consequential events tumbling one after the other. In 1968, just days passed between President Lyndon Baines Johnson’s decision to bow out of his re-election campaign and the assassination of Martin Luther King Jr., which touched off a wave of protest and grief around the nation and reshaped the election.

In September 2008, an economic crisis turned the race upside down — an opportunity that Barack Obama, then a young Democratic senator, seized to portray himself as in charge. In October 2016, a videotape showing Trump speaking crudely about grabbing women’s private parts rocketed around the world. Weeks later, a letter surfaced from the F.B.I. director reopening his investigation into Hillary Clinton’s