Tens of millions of dollars of advertising has not changed President Biden’s polling deficit. Donald J. Trump’s criminal trial has not altered the race’s trajectory. And Mr. Biden’s significant cash and infrastructure advantages have yet to pay political dividends. So on Wednesday, the one weekday Mr. Trump is not confined to a courtroom, the Biden campaign shook up the race, publicly offering to bring forward the first presidential debate by three months. The move was meant to jolt...