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Facing a steep challenge as he prepares to meet with Republican leaders about uniting their splintering party, Donald J. Trump on Monday struck a more conciliatory tone about House Speaker Paul D. Ryan, disavowing an ally’s call for a primary challenge against Mr. Ryan.

Mr. Ryan responded by saying he would step down from his position as chairman of the Republican National Convention in July if that is what the party’s presumptive nominee requests.

After Mr. Ryan, the nation’s highest-ranking elected Republican, said last week that he was “not ready” to endorse Mr. Trump for president, Mr. Trump on Sunday refused to rule out blocking Mr. Ryan from the convention role.

Also on Sunday, one of Mr. Trump’s top supporters, the former Alaska governor Sarah Palin, called for a primary challenge against Mr. Ryan, Republican of Wisconsin.

But by Monday, both Mr. Trump and Mr. Ryan appeared to be backing away slightly from confrontation.

Mr. Trump disavowed any hand in Ms. Palin’s remarks in a morning interview on CNN with Chris Cuomo.

“She’s a terrific person, but she’s very much a free agent and I didn’t know about this until yesterday,” Mr. Trump said. “I guess she’s been fighting, or she’s endorsing somebody that’s running against Paul Ryan, and I didn’t know about it until yesterday when I read about it.”

For his part, Mr. Ryan told a Milwaukee Journal Sentinel columnist, Christian Schneider, “I’ll do whatever he asks me to do,” referring to Mr. Trump. A spokesman for Mr. Ryan, Brendan Buck, said he understood Mr. Schneider’s report to be accurate. Mr. Ryan is the most high-profile member of Congress to say he is not comfortable throwing his support to the presumptive nominee, citing their significant policy differences and the tone of Mr. Trump’s campaign.

Mr. Trump is to meet with Mr. Ryan on Thursday at the Republican National Committee headquarters in two separate meetings – one with the House Republican conference and one with just Mr. Ryan and Reince Priebus, the party chairman and an ally of the speaker.

Mr. Trump spoke warmly of Mr. Ryan on CNN Monday morning.

“I’ve always liked him,” Mr. Trump said. “He called me not so long ago, I don’t know, a number of weeks ago, but he called me and he was very supportive and very nice and I thought everything was fine, and then I got blindsided, so we’ll see.”

Mr. Trump could be facing a tough crowd on Thursday. A number of House Republicans have taken issue with his tone and positions throughout the campaign.

Mr. Ryan has said he might still be able to endorse Mr. Trump, but that he needed to hear more from him.

The meetings may be further complicated by Mr. Trump’s recent statements on fiscal issues.

Mr. Ryan has served as chairman of the House budget committee, and has a strict set of policy views that generally adhere to conservative orthodoxy on issues like taxes and monetary policy. But Mr. Trump seemed to challenge those views in the last week, when he suggested in a string of interviews that he would increase taxes on high earners, that repaying the national debt would not be a problem for Washington “because you print the money” and that he would be open to an increase in the minimum wage, a concept Republicans oppose at the federal level.

In the CNN interview, Mr. Trump – who has made his political mark as the “tell-it-like-it-is” candidate – tried to counter questions that he was flip-flopping on policy issues.

“Let me just set it straight,” Mr. Trump said in talking of his past tax proposals. “I put in the biggest tax decrease of anybody running for office by far, O.K., and many people think it’s great, and if anything, I was criticized because it’s too steep a cut, but that’s O.K., but I put in by far the biggest tax decrease.”

He added, “What I said – and that really is a proposal because we have to go to Congress, we have to go to the Senate, we have to go to our congressmen and women and we have to negotiate a deal. So it really is a proposal, but it’s a very steep proposal.”

Then he said, “I said that I may have to increase the section – and by the way, everybody across the board, businesses, everybody’s getting a tax cut, especially the middle class. And I said that I may have to increase it on the wealthy. I’m not going to allow it to be increased on the middle class. Now, if I increase on the wealthy, that means they’re still going to be paying less than they pay now.”

But he added, “I’m not talking about increasing from this point, I’m talking about increasing from my tax proposal.”