In private, Trump advisers say the campaign now takes a colder and more clinical view of the electoral map. Mr. Trump, Republicans believe, may have even fewer ways to count to 270 than Mr. Romney and Mr. McCain had, because of his debilitating unpopularity with women and nonwhite voters.

Mr. Trump continues to fight at a severe financial and organizational disadvantage against Mrs. Clinton, leaving him without the funds to campaign effectively across all of the states Mr. Romney contested. At the end of June, Mr. Trump had less than half as much cash in reserve as Mrs. Clinton — $20 million to her $44 million.

In several major swing states, Mr. Trump’s campaign has not yet approved final budgets for his state-level operations, according to Republicans in communication with his campaign, leaving Republicans on the state and national levels uncertain about his ability to mount major advertising and get-out-the-vote operations.

And in some of the most crucial states, Mr. Trump continues to face resistance within his own party: In Ohio, he has feuded openly with the popular Republican governor, John Kasich, a former primary opponent who has refused to endorse his campaign. In Florida, some of the most influential Hispanic Republicans in the southern part of the state have withheld their support, hobbling his candidacy there.