Any race that pits Mr. Christie against Mr. Trump is bound to be especially personal. Mr. Trump seemed to find joy in belittling Mr. Christie from the White House; Mr. Christie blamed Mr. Trump for giving him a bout of Covid that left him gravely ill and hospitalized.

In interviews with New Jersey voters, Mr. Christie’s assets and liabilities were repeatedly described as two sides of the same coin.

To moderates thirsty for a centrist voice: He is not Mr. Trump.

And to Trump loyalists who might prefer that Mr. Christie retreat permanently to his beach house in Bay Head, it was much the same refrain: He is not Mr. Trump.

“Anybody in the mix who’s not Trump is good,” David Philips, 64, said Friday during his lunch break in Trenton, the capital, where he has worked as a state construction official for 20 years. He said he tended to vote for Democrats and was never a big fan of Mr. Christie.

“But he’s a reasonable guy compared to Trump,” Mr. Philips said.

After dropping out of the 2016 presidential contest, Mr. Christie became one of Mr. Trump’s biggest boosters. But he is now positioning himself as the teller of hard Trump truths — a perhaps unlikely messenger with a message that will be challenging to sell to a party full of Trump supporters.