“The donor community writ large is beginning to be resigned to Trump and fearful of spending money against him,” said Matt Mackowiak, a Republican consultant based in Texas.

Meanwhile, opinion of Trump among Republican voters is broadening. Peter Brown, assistant director of polling for Quinnipiac University, finds it notable that “the number of voters who say they couldn’t vote for him seems to be dropping a bit.”

“It shows he is also doing something to raise his acceptability,” Brown said.

Another daunting aspect of Trump’s candidacy is his apparent broad appeal across constituencies, according to exit polls from the nominating contests so far. A Trump sweep through Tuesday’s contests, from the evangelical base in the Deep South to the blue-collar regions of Massachusetts and Vermont, will be particularly troubling for his rivals. Cruz has campaigned on consolidating and mobilizing religious conservatives while Rubio has campaigned as the Uniter in Chief, arguing he is the only candidate capable of bringing new and unconventional voters into the fold.