Mr. Trump now feels so empowered that he does not think he needs the political support of the party establishment to defeat the likely Democratic nominee, Hillary Clinton. He is confident that his appeal will be broad and deep enough among voters of all stripes that he could win battleground states like Michigan, Ohio, and Pennsylvania without the support of leaders like Mr. Ryan, Mr. Trump said in an interview on Saturday.

Although he plans to meet with Mr. Ryan and House Republican leaders on Thursday, Mr. Trump said he would not materially change his policies or style to win their endorsements. “Everything is subject to negotiation, but I can’t and won’t be changing much, because the voters support me because of what I’m saying and how I’m saying it,” Mr. Trump said. “The establishment didn’t do anything to make me the nominee, so its support won’t really make much difference in me winning in November.” (Mr. Trump will, though, be somewhat dependent on the party’s fund-raising muscle since he has indicated he will not fully self-finance his general election campaign.)

One reason Mr. Trump takes a skeptical view of establishment support is that he does not believe much in the power of the Republican elite. He is the party’s presumptive nominee, after all, because the political forces that once might have halted his rise have been enfeebled. Leaders such as Mr. Romney warned in the direst terms that Mr. Trump’s nomination would stain the party and lead it to ruin. Venerable media outlets on the right, like National Review, sought to reprise their role as arbiters of who is fit to carry the banner of conservatism. Their pleas fell on deaf ears.

Mr. Trump’s arsenal was far more fearsome. Combining modern-day fame and an age-old demagogy, he bypassed the ossified gatekeepers and appealed directly to voters through a constant Twitter stream that seemed interrupted only by television appearances.

In doing so, he seemed to grasp that a new twist on direct democracy was in the offing: that disaffected voters who tune out the traditional modes of political communication might be reachable through their smartphones, and Twitter messages or Reddits might be more relevant to those voters than the findings of a more scientific poll.

On the left, too, Senator Bernie Sanders has built his own movement with millions of voters, and $210 million in fund-raising, by using online tools as simple as email to seek support. Yet Mr. Trump’s celebrity has been an enormous asset with voters who feel gratified and inspired that he would lavish them with attention and bluntly express some of the ideas and attitudes they share.