Democrats are turning up the heat on John McCain in the one area that's been relatively sacred this campaign season -- military commitment.

Even as newly released medical records highlight the ailments McCain continues to suffer, stemming from his days as a prisoner of war in Vietnam, the presumptive GOP nominee is catching more flak for sitting out the vote on the GI bill expansion Thursday.

The measure would guarantee full college scholarships for those who serve in the military for three years.

"If our veterans want to go to college, they should be able to do so the minute their boots hit the ground," says John Boccieri, an Air Force Reserve major and Ohio state senator, in the Democrats' weekly radio address -- in which McCain is a frequent target.

The Democratic Party released an early version of their radio address Friday, timed as millions of Americans head into Memorial Day weekend.

"Sadly, President Bush has threatened to veto the (GI) bill. Senator John McCain, who hopes to take his place, not only opposed it, but when given the opportunity to support his fellow veterans on the eve of Memorial Day weekend, didn't even show up to vote nor express his concerns," Boccieri says. " ... vetoing this measure will send a clear message that politics has defeated patriotism."

The address was released after Barack Obama chided McCain Thursday during a Senate debate on the GI bill.

"I respect Senator John McCain's service to our country. ... but I can't understand why he would line up behind the president in opposition to this GI bill. I can't believe he believes it is too generous to our veterans," Obama said Thursday. "I could not disagree with him and the president more on this issue. There are many issues that lend themselves to partisan posturing but giving our veterans the chance to go to college should not be one of them."

That prompted a nasty exchange between the two likely general election opponents.

McCain released a statement saying he was concerned the bill would discourage people from re-enlisting and cut retention rates -- and then he took a swipe at Obama for not serving in the military himself.

"I will not accept from Senator Obama, who did not feel it was his responsibility to serve our country in uniform, any lectures on my regard for those who did," McCain said.

Obama and McCain have traded charges recently on everything from their foreign policy differences to the influence of lobbyists in their campaigns.

Obama has practically abandoned criticism of Hillary Clinton as he moves closer to securing the Democratic nomination.

But Republican strategist Chip Saltsman said McCain's military record might not be the best political fodder for Democrats.

"This is bad politics and bad policy for Barack Obama," he told FOX News. "It was a cheap shot, it was on the Senate floor and I think it backfired on him."

Democratic strategist Julia Piscitelli said Obama wasn't really targeting McCain's military record, but rather his alignment with President Bush on the Iraq war.

In the Democratic radio address, Boccieri also went after McCain for saying he's willing to keep a troop presence for "100 years."

"We need strong leaders in Washington who will bring our troops home from Iraq safely, honorably and soon. Neither President Bush nor John McCain has offered an exit strategy," he says.

The Democratic-led Senate on Thursday passed the GI bill, sponsored by Sen. Jim Webb, D-Va., and supported by Obama, on a 75-22 vote as 25 Republicans abandoned President Bush, who opposed it.

Obama and his rival, Hillary Clinton, returned to Washington for the vote. McCain stayed in California to campaign and raise money.

The Associated Press contributed to this report.