Mr. Trump’s comments, in an interview with George Stephanopoulos of ABC News that will air on Sunday, were his most extensive remarks since Khizr Khan delivered on Thursday one of the most powerful speeches of the convention in Philadelphia. In it, Mr. Khan spoke about how his 27-year-old son, Humayun Khan, an Army captain, sacrificed his life in a car bombing in 2004 in Iraq as he tried to save other troops.
He criticized Mr. Trump, saying he “consistently smears the character of Muslims,” and pointedly challenged what sacrifices Mr. Trump himself had made. Mr. Khan’s wife, Ghazala, stood silently by his side.
Mr. Trump, the Republican presidential nominee, told Mr. Stephanopoulos that Mr. Khan seemed like a “nice guy” and that he wished him “the best of luck.” But, he added, “If you look at his wife, she was standing there, she had nothing to say, she probably — maybe she wasn’t allowed to have anything to say, you tell me.”
The comment implied that she was not allowed to speak because of female subservience that is expected in some traditional strains of Islam. Mr. Trump also told Maureen Dowd of The New York Times on Friday night, “I’d like to hear his wife say something.”
The negative remarks about the mother of a dead soldier drew quick and widespread condemnation, and even given Mr. Trump’s history of retaliating when attacked, they were startling. They called to mind one of his earliest thrusts of the campaign, when he responded to criticism from Senator John McCain of Arizona, once a prisoner of war in Vietnam, by saying at an Iowa forum, “I like people that weren’t captured.”
But Mr. McCain has a long history in the public eye. The Khans, before their convention appearance, had spent no time in the public eye.
In an interview on Saturday, Mr. Khan lashed out at Mr. Trump, saying, “He is devoid of feeling the pain of a mother who has sacrificed her son.”
“Trump is totally void of any decency because he is unaware of how to talk to a Gold Star family and how to speak to a Gold Star mother,” said Mr. Khan, referring to the term for surviving family members of those who died in war.
He said his wife did not talk on Thursday because she finds it too painful to speak about her son’s death. Ms. Khan herself spoke publicly on Friday to MSNBC’s Lawrence O’Donnell, saying she “cannot even come in the room where his pictures are.”
When she saw her son’s photo on the screen behind her on the stage in Philadelphia, she said, “I couldn’t take it.”
“I controlled myself at that time,” she said. “It is very hard.”
In his interview with The New York Times, Mr. Khan said his wife did help him craft the remarks, and even told him to remove certain attacks he had wanted to make against Mr. Trump.
But on Saturday, he unmuzzled himself.
“Unlike Donald Trump’s wife, I didn’t plagiarize my speech,” Mr. Khan said, referring to how several lines from a Michelle Obama speech found their way into Melania Trump’s address at the Republican convention.
“I also wanted to talk about how he’s had three wives, and yet he talks about others’ ethics and their religion,” Mr. Khan said. “I wanted to say 10 other things about him, and she said, ‘Don’t go to his level. We are paying tribute to our son.’”
Mr. Trump’s comments provoked another avalanche of criticism on social media, and again put Republican leaders in a difficult position, facing fresh demands that they repudiate their presidential nominee.
Even before Mr. Trump’s remarks to ABC News, Mr. Khan had asked that Senator Mitch McConnell, the majority leader, and Paul D. Ryan, the House speaker, denounce Mr. Trump.
Don Stewart, a spokesman for Mr. McConnell, said on Saturday he had not seen Mr. Trump’s latest remarks, but referred to Mr. McConnell’s response late last year that a ban on Muslims entering the United States, proposed by Mr. Trump, would be unacceptable.
In the same interview, when Mr. Stephanopoulos said that Mr. Khan had pointed out that his family would not have been allowed into the United States under Mr. Trump’s proposed ban, the candidate replied, “He doesn’t know that.”
And when asked what he would say to the grieving father, Mr. Trump replied, “I’d say, ‘We’ve had a lot of problems with radical Islamic terrorism.’”
Mr. Stephanopoulos also noted that Mr. Khan said that Mr. Trump had “sacrificed nothing,” and had lost no one.
“Who wrote that? Did Hillary’s scriptwriters?” Mr. Trump replied. “I think I’ve made a lot of sacrifices. I’ve worked very, very hard. I’ve created thousands and thousands of jobs.”
Reihan Salam, a conservative writer for National Review and a frequent Trump critic, said that the candidate had an opportunity to declare remorse for the Khans while still holding to his own views as a candidate.
“A more skillful communicator would have avoided comparing his sacrifice to that of a parent who had lost his adult son to violence in Iraq, for the obvious reason that there’s no way to win,” he said. “Instead, he might have asked why Humayun Khan had died in the first place — because of a war that many if not most Americans regard as a tragic blunder, that led to the deaths of thousands of Americans.”
“There was really no benefit for Trump in suggesting that Ghazala Khan had been muzzled, because she could easily come out and say that she had been too grief-stricken to speak, which she did.”
Tim Miller, a former communications director for Jeb Bush’s presidential campaign, called Mr. Trump’s comments “inhuman.”
Ibrahim Hooper, the spokesman for the Council on American-Islamic Relations, said on Saturday: “It’s really despicable that anyone, let alone a presidential candidate, would choose to dishonor the service of an American who gave his life for this nation.”
Ms. Khan, he said, “was obviously there to support her husband who was offering what many people believe was the most impactful speech of the entire convention.”
“And you know,” Mr. Hooper said, “to just completely throw that away, what does that say about what Trump would be like as president?”
As is often the case, Mr. Trump, who has had no campaign events this weekend, managed with a few words to upstage his opponent, Hillary Clinton, who was making several stops in Ohio and Pennsylvania with her running mate, Senator Tim Kaine of Virginia.
“I was very moved to see Ghazala Khan stand bravely and with dignity in support of her son on Thursday,” Mrs. Clinton said Saturday in a relatively reserved statement. “This is a time to honor the sacrifice of Captain Khan and all the fallen.”
In the ABC News interview, Mr. Trump also hedged over whether he would participate in the three scheduled debates with Mrs. Clinton. He insinuated that she had worked to schedule two of the debates during football games so viewership would be lower.
He also said the National Football League had sent him a letter complaining about debate dates.
The debates were scheduled last September by the bipartisan Commission on Presidential Debates. And while Joe Lockhart, a spokesman for the National Football League, said the league was not happy about the scheduling, “we did not send a letter to Trump.”