Michael Waltz in one of the anti-Donald Trump ads. American Future Fund Military veterans are appearing in ads released over the weekend by an outside group, hoping to stop Donald Trump from snagging the GOP presidential nomination.

The ads, from the conservative American Future Fund, feature veterans disavowing Trump's statements about prisoners of war and end with the text: "Trump's a phony. Stop him now."

In one ad, former Special Forces commander Michael Waltz, who served in Afghanistan, said that Trump "hasn't served this country a day in his life" and called him a Vietnam War draft-dodger.

"He essentially called anyone who is captured in combat a loser," Waltz said. "It's something that I just personally can't stomach and am sickened by, as should every veteran and every soldier in the United States military."

Trump, who is the clear frontrunner for the Republican nomination, criticized Arizona Sen. John McCain last year and called into question his status as a "war hero."

"He's not a war hero," Trump said. "He's a war hero because he was captured. I like people that weren't captured."

Trump quickly walked back that statement and agreed that McCain, a Vietnam War POW, was in fact a war hero. Trump also said that he doesn't like "losers," referring to McCain's loss to President Barack Obama in the 2008 presidential election.

In another ad from American Future Fund, a retired lieutenant colonel who served in Vietnam echoed the criticisms of Trump's statements about McCain.

"When I heard Donald Trump insult my fellow prisoners of war from Vietnam by calling us losers, that was the most infuriating comment I think I've heard from a politician in my entire life," Tom Hanton said. He was a prisoner of war in Vietnam from 1972 to 1973.

"Trump would not have survived a POW experience," Hanton said. "He would have been probably the first one to fold."

The ads also called on voters to look into Trump's record.

Outside groups have been ramping up spending recently as Trump continues racking up primary and caucus wins across the country. The American Future Fund has spent $2 million so far in Florida and Illinois, according to The New York Times.

Watch the ads below: