MIAMI  — President Donald Trump emphatically rejected claims Wednesday that he was disrespectful to the grieving family of a slain soldier, as the firestorm he ignited over his assertions of empathy for American service members spread into a third contentious day. “I have proof,” he insisted.

The controversy over how Trump has conducted one of the most sacred of presidential tasks generated new turmoil in the White House and left chief of staff John Kelly, a retired Marine general whose son was killed in Afghanistan, angry and frustrated at the way the issue has become politicized. It was fresh evidence of Trump’s willingness to attack any critic and do battle over the most sensitive of matters.

The aunt of an Army sergeant killed in Niger, who raised the soldier as her son, said Wednesday that Trump had shown “disrespect” to the soldier’s loved ones as he telephoned them to extend condolences as they drove to the Miami airport to receive his body. Sgt. La David Johnson was one of four American soldiers killed nearly two weeks ago; Trump called the families on Tuesday.

Rep. Frederica Wilson, a Florida Democrat who was in the car with Johnson’s family, said the president told the widow that Johnson “knew what he signed up for.”

She said the president told them something along the lines of “you know this is possible when you sign up but it still hurts.”

Cowanda Jones-Johnson, who raised the soldier from age 5 after his mother died, told The Associated Press on Wednesday that the Democratic congresswoman’s account was correct.

“Yes the statement is true,” she said. “I was in the car and I heard the full conversation.”

At the airport, widow Myeshia Johnson leaned in grief across the flag-draped coffin after a military guard received it.

“She was crying for the whole time,” Wilson said. “And the worst part of it: When he hung up you know what she turned to me and said? She said he didn’t even remember his name.”

Trump started the storm this week when he claimed that he alone of U.S. presidents had called the families of all slain soldiers.

AP found relatives of four soldiers who died overseas during Trump’s presidency who said they never received calls from him. Relatives of three also said they did not get letters. And proof is plentiful that Obama and George W. Bush — saddled with far more combat casualties than the roughly two dozen so far under Trump — took painstaking steps to write, call or meet bereaved military families.

Chris Baldridge, the father of Army Cpl. Dillon Baldridge who was killed in June in Afghanistan, told The Washington Post that when Trump called him, he offered him $25,000 and said he would direct his staff to establish an online fundraiser for the family. But Baldridge said it didn’t happen.

The White House said Wednesday that a check has been sent. And Trump spokeswoman Lindsay Walters said it was “disgusting” that the news media were casting his “generous and sincere gesture” in a negative light.

White House press secretary Sarah Huckabee Sanders said protocol requires that the Pentagon and White House Military Office prepare and confirm an information packet before the president contacts grieving family members, a process that can take weeks. She said Trump has made some form of contact with every family for whom he has received the appropriate information.

Trump, who tangled with a Gold Star family during last year’s presidential campaign, fiercely denied Rep. Wilson’s version of events. He declared on Twitter: “Democrat Congresswoman totally fabricated what I said to the wife of a soldier who died in action (and I have proof). Sad!”

He later insisted that he “didn’t say what that congresswoman said, didn’t say it at all. She knows it.”

In private, he bitterly complained to associates about the flare-up, believing the press was eager to paint his response in a negative light, according to two people who recently spoke to him but were not authorized to comment publicly about private conversations. His anger was echoed from the White House briefing room podium by Sanders, who said she was “appalled” by what she described as Wilson’s efforts to politicize the tragedy.

“Just because the president said ‘your guy’ doesn’t mean he doesn’t know his name,” said Sanders. She added that while no recordings of the conversation existed, several senior officials, including Kelly, witnessed the call and described Trump’s manner as “respectful” and “very sympathetic.”

Wilson did not back down from her account.

Like presidents before him, Trump has made personal contact with some families of the fallen but not all. What’s different is that Trump, alone among them, has suggested he’s done a better job of honoring the war dead and their families. He said Tuesday: “I think I’ve called every family of someone who’s died” while suggesting past presidents had not.