The repudiation of the election-denying wing of the party by other Republicans in Michigan represents rare public pushback from conservatives against Mr. Trump’s attempts to force candidates across the country to support his claims of a rigged 2020 vote. That stance has become a litmus test for G.O.P. politicians up and down the ballot as Mr. Trump adds to his slate of more than 150 endorsements this election cycle.

Yet some Republicans in Michigan and beyond worry that a singular, backward-looking focus on the 2020 election is a losing message for the party in November.

“Rather than distancing themselves from this undisciplined loser,” Mr. Daunt wrote in his resignation letter, “far too many Republican ‘leaders’ have decided that encouraging his delusional lies — and, even worse — cynically appeasing him despite knowing they are lies, is the easiest path to ensuring their continued hold on power, general election consequences be damned.