McCain, the all-but-nominated Republican presidential candidate, opposes a Democratic-backed bill that would significantly expand the breadth of education benefits for veterans, first adopted for those returning from World War II. Democrats want the proposal included in a war spending bill the Senate is scheduled to vote on this week.
Sen., McCain's most likely general election opponent, already has raised objections to McCain's resistance. And on Tuesday, a veterans' group that has been critical of the war in Iraq is launching an ad in Washington to pressure McCain to change his mind.
By taking issue with McCain on the subject of veterans, Democrats hope to weaken one of his biggest assets - his personal biography as a former Navy pilot who became a prisoner of the North Vietnamese and endured torture at the hands of his captors.
The legislation, sponsored by Democratic Sen. Jim Webb of Virginia and Republican Sen. Chuck Hagel of Nebraska, also veterans of Vietnam, would guarantee full tuition payments to veterans at any public school in their home state. Its expected cost is $52 billion over 10 years.
McCain says the legislation is too expensive and has proposed his own version, which would increase the monthly benefit available to most veterans to $1,500 from $1,100. It would not offer the equivalent of a full scholarship.
The ad by VoteVets.org Action Fund, features Iraq and Afghanistan veterans noting that both McCain and President Bush oppose the bill.
"McCain thinks covering a fraction of our education is enough," one veteran says. Another one, pictured recovering from head wounds, adds in a voiceover: "We didn't give a fraction in Iraq. We gave 100 percent."
"Senator McCain" an announcer concludes, "we respect your service. Please respect ours."
The ad is running Tuesday and Wednesday on broadcast and cable television stations in Washington, primarily during news broadcasts. VoteVets is running a similar ad targeting Sen. John Cornyn, R-Texas, in San Antonio and Waco - two Texas markets with military bases.
Other veteran's groups - from Veterans of Foreign Wars to the American Legion - support the Democratic bill. But VoteVets, which has been aggressive in its criticism of Bush's war policies, is the first to take McCain on directly.
"He's trying to run interference for the White House with a watered down bill," said Jon Soltz, an Iraq war veteran and chairman of VoteVets.org. "How could this not be an issue in the presidential campaign if he doesn't vote for this bill? There is no way for this to go away if he votes against it."
VoteVets is a nonprofit corporation and part of a Democratic-leaning coalition of war critics that has vowed to spend millions linking McCain to Bush's war policies. Earlier this year, VoteVets ran an ad on Washington cable stations urging McCain to abandon his commitment to Iraq.
The Pentagon opposes the Webb-Hagel bill, saying the benefit could hurt retention by encouraging members of the military to leave after serving only three years.
Obama, campaigning in West Virginia last week, said the bill is necessary to make veteran's benefits match the rising costs of tuition.
"I have great respect for John McCain's service to this country and I know he loves it dearly and honors those who serve," Obama said. "But he is one of the few senators of either party who oppose this bill because he thinks it's too generous. I couldn't disagree more."