The horrible assassination attempt on Donald Trump has underscored Joe Biden’s dire political situation. Americans hope the awful events in Butler, Pa., will inspire the reversal of our ever-coarsening political culture, as Mr. Biden called for on Sunday night. It’s now Mr. Trump’s turn, and his moment, to answer that call with a more unifying vision as his party meets this week in Milwaukee.

Nonetheless, politics will march forward — and have no doubt, Mr. Biden is losing this race. The decision by leaders of the Democratic National Committee to ratchet up the calendar and try to confirm him as the party’s nominee before the convention only adds to the feeling of desperation that surrounds him.

Democrats and other Trump opponents know this and most are in full panic. A Republican convention that celebrates the party nominee surviving a would-be assassin’s bullet while also drawing a stark and, we can say it, opportunistic contrast between a vibrant Donald Trump and an aging Joe Biden will be a success for the Republicans. Democrats are in for a very long political week.

The total war between Mr. Trump and Mr. Biden has now raged for eight years and exhausted our nation. I’ve been proud to be on Joe Biden’s side in that war, despite my conservatism and my years of proudly working for the pre-Trump G.O.P. But America needs a fresh path forward. Joe Biden cannot offer that. A new candidate, a centrist Democrat, could.

Mr. Biden now faces that grim reaper of politics: If you are perceived as a certain loser, you will become one. Campaign psychology is based on fear. While a candidate’s supporters will boast, bluster and project steely confidence, deep down they share the same quiet terror: “What if we … lose?”

Among Democrats, the terror isn’t quiet anymore. The grim specter of a President Trump once again lurching around the Oval Office has made the thought of losing this election especially horrifying .