"Now, let me be clear: No one can dispute John McCain's love for this country or his concern for veterans. But here's what I don't understand. I don't understand why John McCain would side with George Bush and oppose our plan to make college more affordable for our veterans," the Democratic presidential candidate said. "George Bush and John McCain may think our plan is too generous. I could not disagree more."
Obama's criticism renews a clash that turned personal after the Senate approved the scholarship bill Thursday.
During the Senate debate, the Illinois senator questioned why McCain - a Navy veteran and former prisoner of war - would oppose the measure.
McCain responded with a sharp statement saying that he wouldn't listen to any lectures on veterans' affairs from Obama, "who did not feel it was his responsibility to serve our country in uniform."
The Arizona senator opposes the scholarship measure, as does the Pentagon, because it applies to people who serve just three years. He fears that would encourage people to leave the military after only one enlistment even as the U.S. fights two wars and is trying to increase the size of the Army and Marine Corps.
Instead, McCain and Republican colleagues proposed a bill to increase benefits in conjunction with a veteran's length of service. Senate Democrats blocked that measure.
"While Barack Obama engages in the same tired partisan politics that has failed our veterans time and again, John McCain has offered legislation that will expand needed education benefits for veterans while promoting retention in our armed forces," McCain spokesman Brian Rogers responded Saturday to Obama's remarks.
Only three primaries are left in the battle for the Democratic nomination, and Puerto Rico is holding one of them. After his speech, Obama was headed to a town hall-style meeting with voters in Old San Juan. Rival Hillary Rodham Clinton also had a town-hall event in Puerto Rico scheduled for later Saturday. Both candidates are hoping to increase their share of the 55 delegates who will be chosen June 1.
Puerto Ricans can vote in party primaries but not in the fall general election.