Who could actually replace Biden? We break down the options.

President Joe Biden’s posture hasn’t changed since his disastrous debate performance: He’s staying in the race.

He insisted in an interview with ABC’s George Stephanopoulos that it would take “the Lord Almighty” to pull him out of his rematch with former President Donald Trump. And on Monday, he expressed his frustration in a surprise call into MSNBC’s “Morning Joe,” daring his critics to run against him.

But other Democrats — voters, donors and elected officials — are far less sure. And as several senior House Democrats have called on Biden to step down, and with Congress...