Republican Donald Trump told a motorcycle rally on Sunday that people in the U.S. illegally often are cared for better than the nation's military veterans, without backing up his allegation.

"Thousands of people are dying waiting in line to see a doctor. That is not going to happen anymore," Trump told veterans gathered in front of the Lincoln Memorial as part of the annual Rolling Thunder event, which brings thousands of motorcyclists to Washington each Memorial Day weekend.

Trump has repeated his comparison of the treatment of immigrants and veterans frequently during the campaign. Congress and many states have written an assortment of laws and policies designed to restrict government services to people living in the country illegally.

The Veterans Affairs Department, meanwhile, has come under criticism and congressional scrutiny for a number of failures, from cutting off benefits of thousands of veterans who were wrongly declared dead to chronically long wait times for medical services at VA health care sites. As many as 40 patients died while awaiting care at the Phoenix VA hospital alone.

The Rolling Thunder event is organized to draw attention to veterans' issues and dedicated to remembering prisoners of war and service members missing in action.

"We're with you 100 percent," Trump told the crowd.

Trump, now the presumptive Republican nominee for president, angered veterans last year when he said he liked "people who weren't captured" in wars. That had been a dig at Sen. John McCain, R-Ariz., the party's 2008 nominee, who had been captured and held for more than five years during the Vietnam War after his plane was shot down. Trump claimed that McCain was a "war hero because he was captured."

Trump quickly tried to walk back the comment but has refused to apologize to McCain.

Many veterans groups were furious, but since then Trump has worked to try to repair the damage. He frequently honors veterans at his rallies, and he has come out with a plan to overhaul the Department of Veterans Affairs. He also held a fundraiser for veterans' causes in place of an Iowa debate that he skipped.

Still, Trump, who avoided the draft through a series of deferments, drew scrutiny for not immediately distributing the $6 million he'd claimed to raise, including $1 million he'd pledged himself. He is expected to hold a news conference Tuesday to announce the names of the charities selected to receive the money.

Rolling Thunder spokeswoman Nancy Regg estimated Sunday's event drew about 5,000 people — smaller than the crowds Trump typically attracts. The large plaza between the Lincoln Memorial and the Reflecting Pool on the National Mall had large, empty pockets with no long lines for security, despite the thousands of bikers in town for the group's ride from the Pentagon and through the streets of Washington.

Trump, who frequently boasts about his crowd size, however, claimed that 600,000 people were outside trying to get in.

"I thought this would be like Dr. Martin Luther King, where the people would be lined up from here all the way to the Washington monument, right? Unfortunately, they don't allow 'em to come in," Trump complained as he finished up his speech.

Trump's comments on McCain were also on the minds of many at the event, including John LeBoutillier, a former New York congressman who spoke at the event.

LeBoutillier said Trump "got a little twisted up" with his anger when he spoke about McCain, but said the comment was "totally justified."

"There has never been a public official who's been worse on the POW issue than John McCain," he said.

McCain, in fact, has a long record of supporting veterans' issues in Congress. Most recently, he was instrumental in the passage of landmark legislation to overhaul the Department of Veterans Affairs to alleviate the long delays in getting care, and another aimed at reducing a suicide epidemic among military veterans. He has also pushed for the VA to do more to fire poor-performing employees.

"Sen. McCain has made veterans issues, specifically fixing the broken VA health care system, one of his top priorities," McCain spokeswoman Rachael Dean said in an email. "However, Sen. McCain is the first to argue there is still work to be done — the VA system is painfully bureaucratic, slow to change and to react."

Still, LeBoutillier's sentiment was echoed by veterans, including Mike Sukeena, who said that he'd discussed Trump's comment with his fellow veterans.

"McCain was a prisoner of war, but I don't know — I think he's deserted the veterans, I really do," said Sukeena, 72, who served in Vietnam during his six years in the Navy, and now lives in Manassas, Virginia. "All of them have turned their back on the veterans."

Sukeena said at first he was dismayed by the comment but no longer holds it against Trump and plans to vote for the candidate.

"I like the fact that he's going to make America great again and that he's going to work for our veterans," he said.