The Washington Post’s Philip Rucker explains how unusual it is that Republican presidential nominee Donald Trump is withholding his endorsements of House Speaker Paul D. Ryan and Sen. John McCain (R-Ariz.) in their primary races. (Bastien Inzaurralde/The Washington Post)

Republican presidential nominee Donald Trump escalated his war with his own party’s leadership Tuesday by refusing to endorse House Speaker Paul D. Ryan or Sen. John McCain, two of the GOP’s highest-ranking elected officials, in their primary campaigns.

Trump’s comments — an extraordinary breach of political decorum that underscores the party’s deep divisions — came as President Obama delivered his sternest rebuke yet of the celebrity mogul candidate. Obama declared Trump “unfit to serve as president” and “woefully unprepared to do this job,” and he challenged Republican leaders to withdraw their support of their nominee.

Obama punctuated his remarks, delivered at a Tuesday morning news conference, by explaining that he had never before felt compelled to so thoroughly denounce a political opponent. While he recalled disagreeing with McCain and Mitt Romney on policy issues in the 2008 and 2012 campaigns, Obama said that he never questioned their qualifications or their “basic decency,” and that he knew they would “abide by certain norms and rules and common sense. But that’s not the situation here.”

In an interview with The Washington Post on Tuesday, Trump said he was not backing Ryan in his primary election next Tuesday in Wisconsin, or McCain in his Arizona primary later this month. Both have endorsed Trump but have criticized some of his policies and statements, most recently his belittling of the parents of dead U.S. Army Capt. Humayun Khan.

Trump praised Ryan’s underdog opponent, Paul Nehlen, for running “a very good campaign” and said of Ryan: “I like Paul, but these are horrible times for our country. We need very strong leadership. We need very, very strong leadership. And I’m just not quite there yet. I’m not quite there yet.”

Trump’s comments underscore the continuing divisions in the GOP two weeks after the party’s national convention in Cleveland, which was carefully choreographed to showcase unity. Also Tuesday, Rep. Richard L. Hanna (N.Y.) became the first sitting Republican member of Congress to declare publicly his plans to vote for Democratic nominee Hillary Clinton.

Trump said that Ryan has sought his endorsement but that he is only “giving it very serious consideration.” Responding to Trump, Ryan spokesman Zack Roday said in a statement: “Neither Speaker Ryan nor anyone on his team has ever asked for Donald Trump’s endorsement. And we are confident in a victory next week regardless.”

Trump made his comments during a wide-ranging 50-minute interview Tuesday afternoon over lunch at the Trump National Golf Club in Northern Virginia.

He said he will work to negotiate the terms of general-election debates in his favor, saying that three is “the right number” but that they should not be scheduled on the same nights as National Football League games or the baseball World Series. He said that he should have influence in selecting “a fair moderator” for each debate and that third-party candidates Gary Johnson and Jill Stein should not be allowed on stage. “I’d rather have head to head” with Clinton, Trump said.

He took issue with the characterization of Clinton at last week’s Democratic National Convention as a fighter and a change-maker. “Hillary’s not a change person. She’s going to be a person to keep it just the way it is,” Trump said, biting into his cheeseburger. “It’s going to be four more years of Obama.”

Trump lashed out at the media, including The Post, which he accused of turning sharply against him since he secured the nomination. “It’s myself really against the media,” he said, citing what he views as “a tremendous bias against me.”

Trump’s statements about Ryan are the latest hiccup in what has been a fraught relationship for the two party leaders. Ryan endorsed Trump this spring and spoke on his behalf at the convention, but only after a period of public soul-searching.

Ryan has disagreed with Trump on several key issues — including his proposed temporary ban on Muslims entering the United States — and he issued a statement over the weekend that indirectly criticized Trump’s comments about the Khans.

“Many Muslim Americans have served valiantly in our military, and made the ultimate sacrifice,” Ryan said in the statement. “Captain Khan was one such brave example. His sacrifice — and that of Khizr and Ghazala Khan — should always be honored. Period.”

Khizr Khan spoke at the Democratic convention with his wife, Ghazala, at his side. He said that Trump “smears the character of Muslims” and challenged his knowledge of the Constitution. The Khans have sat for numerous interviews in the days since, calling Trump’s character into question.

In the Tuesday interview, Trump defended his commentary about the Khans by saying, “I was viciously attacked on the stage, and I have a right to answer back.”

However, his campaign acknowledged the crisis in an email sent to congressional supporters this week with the subject line “Urgent Pivot: Khan and TPs.” The email asked allies on Capitol Hill to defend Trump’s heavily criticized remarks about the Khans by underscoring his commitment to ending “radical Islamic terror” and deemphasizing his most confrontational comments.

In the interview, Trump rejected the suggestion that some people have concluded that he lacks common decency. “I think frankly a lot of people agree with what I’m saying,” he said. “I was viciously attacked on the stage. All I did was respond to it. Pure and simple. It should’ve been a one-hour story, and they make it a longer story.”

He blamed what he called “unfair media” for giving the Khans a platform.

Nehlen, Ryan’s primary opponent, came to Trump’s defense over his confrontation with the Khans, for which Trump thanked him in a tweet Monday night. Trump’s shout-out sparked speculation that he might endorse Nehlen.

Asked about this in the interview, Trump said Ryan’s “opponent is a big fan of what I’m saying — big fan. His opponent, who’s running a very good campaign, obviously, I’ve heard — his opponent sent me a very scholarly and well-thought-out letter yesterday, and all I did was say thank you very much for your very nice letter.”

In making his comments Tuesday, Trump may have been seeking retribution for Ryan’s dragging his feet about endorsing Trump in May. Trump’s phrasing of his uncertainty about Ryan — “I’m just not quite there yet” — echoes what Ryan told CNN’s Jake Tapper in a May interview about endorsing Trump: “I’m just not ready to do that at this point. I’m not there right now.”

On Monday, McCain, a Vietnam War hero, issued a lengthy statement denouncing Trump for his comments about the Khan family. Asked about McCain’s rebuke, Trump said, “I haven’t endorsed John McCain.

“I’ve never been there with John McCain because I’ve always felt that he should have done a much better job for the vets,” Trump continued. “He has not done a good job for the vets, and I’ve always felt that he should have done a much better job for the vets. So I’ve always had a difficult time with John for that reason, because our vets are not being treated properly. They’re not being treated fairly.”

McCain did not comment on Trump’s remarks Tuesday. But he did meet with Trump’s running mate, Indiana Gov. Mike Pence, who was in Arizona on Tuesday for two rallies.

McCain is locked in a three-way primary — the election is Aug. 30, and early voting begins this week — against former state senator Kelli Ward and tea party activist Clair Van Steenwyk. A third challenger, Alex Meluskey, suspended his campaign this week.

In the interview, Trump said he thought it was a mistake for senators to distance themselves from him because of his popularity with the Republican base. He singled out Sen. Kelly Ayotte — who, like Ryan and McCain, criticized his comments about the Khans — as a weak and disloyal leader in New Hampshire, a state whose presidential primary Trump won handily.

“New Hampshire is one of my favorite places,” Trump said. “You have a Kelly Ayotte who doesn’t want to talk about Trump, but I’m beating her in the polls by a lot. You tell me. Are these people that should be representing us, okay? You tell me.”

He continued: “I don’t know Kelly Ayotte. I know she’s given me no support — zero support — and yet I’m leading her in the polls. I’m doing very well in New Hampshire. We need loyal people in this country. We need fighters in this country. We don’t need weak people. We have enough of them. We need fighters in this country. But Kelly Ayotte has given me zero support, and I’m doing great in New Hampshire.”

Ayotte, whose aides said she still plans to vote for Trump, responded with a statement: “I call it like I see it, and I’m always going to stand up for our military families and what’s best for the people of New Hampshire.”

Trump went on to say that if he loses the election, he will start two or three “anti-certain candidate” super PACs, which he vowed to fund with $10 million apiece, to savage Republicans or Democrats of his choosing in future elections. He said his targets might include Sen. Ted Cruz (Tex.) or Ohio Gov. John Kasich, who both lost in the primaries to Trump but are eyeing another run in 2020.

Hanna, a three-term congressman who is not running for reelection this year, has bucked his party in the past on issues including same-sex marriage and climate change. He said Trump’s prolonged feud with the Khans was the final straw that pushed him to declare his support for Clinton.

“I saw that and felt incensed,” Hanna told “I was stunned by the callousness of his comments.”

If the Republican disunity is alarming Trump, he did not show it in the interview. He predicted that he would “do great” in Ohio and Pennsylvania, where Clinton and running mate Tim Kaine campaigned together over the weekend.

“I’m going to do great in states that some people aren’t even thinking about,” Trump said. “I’ve got states that we can win that other Republican candidates wouldn’t even stop over for dinner.”

Asked which states he had in mind, Trump paused.

“Well,” he said. “I’d rather not say. . . . That’s my attitude on the military. I don’t like telling the enemy what I’m doing.”

Lateshia Beachum, Callum Borchers, Mike DeBonis, Karoun Demirjian, Michelle Ye Hee Lee, Kelsey Snell, Isaac Stanley-Becker, Sean Sullivan, David Weigel and Katie Zezima contributed to this report.