ALBUQUERQUE, New Mexico (CNN) -- Sen. John McCain on Monday defended his opposition to a Democratic bill that would expand education benefits for veterans, saying it would hurt the military that he hopes to lead.
Sen. John McCain is co-sponsoring alternative legislation to the GI Bill that the Senate passed last week.
The new GI Bill being debated in Congress would expand education benefits for veterans who served at least three years in the military after the September 11, 2001, attacks.
The bill's main sponsor, Sen. Jim Webb, is a Virginia Democrat and, like McCain, a Vietnam War veteran. The Senate passed Webb's bill 75-22 last week. McCain was not in Washington for the vote.
Democrats have targeted McCain for his opposition to the Webb legislation. Watch McCain talk about the U.S. debt to veterans
Saying he takes "a back seat to no one in my affection, respect and devotion to veterans," McCain said Webb's bill would be a disincentive for service members to become noncommissioned officers, which he called "the backbone of all the services."
"In my life, I have learned more from noncommissioned officers I have known and served with than anyone else outside my family," McCain said at a Memorial Day event in Albuquerque.
"They are very hard to replace. Encouraging people to choose to not become noncommissioned officers would hurt the military and our country very badly."
A former Navy officer, McCain was a prisoner of war during Vietnam.
McCain, along with Sens. Lindsey Graham of South Carolina and Richard Burr of North Carolina, has introduced an alternative bill that would increase education benefits on a sliding scale based on an individual's years of service. McCain argues his bill would have a smaller impact on retention rates than the legislation that the Senate passed.
"The office of president, which I am seeking, is a great honor indeed, but it imposes serious responsibilities," the presumptive GOP nominee said.
"I can only tell you, I intend to deserve the honor if I am fortunate to receive it, even if it means I must take politically unpopular positions at times and disagree with people for whom I have the highest respect and affection."
Over the weekend, Sen. Barack Obama, who appears to be the likely Democratic nominee, again tried to tie McCain to Bush by noting that both of them oppose the GI Bill expansion.
"I revere our soldiers and want to make sure they are being treated with honor and respect," Obama said Saturday. "I think the GI Bill is one way for us to do that, and I hope that John McCain and George Bush decide they believe the same thing."
Sparring between McCain and Obama over the GI Bill got personal last week when McCain said he would not be lectured from someone "who did not feel it was his responsibility to serve our country in uniform."
Obama hasn't served in the military.
Referring to Iraq in his closing comments Monday, McCain said he recognized Americans have grown tired of the war and the mistakes made, "but we cannot react to those mistakes by embracing a course of action that will be an even greater mistake, a mistake of colossal historical proportions."
"We must give Gen. [David] Petraeus and the Americans he has the honor to command adequate time to salvage from the wreckage of our past mistakes a measure of stability for Iraq and the Middle East, and a more secure future for the American people," he said.
Later Monday, McCain will attend a fundraiser in Albuquerque.
On Tuesday, President Bush will fly to Phoenix, Arizona, for a fundraiser at a private residence. Bush has been one of the Republican Party's most prolific fundraisers, and McCain will need help to keep up with Democratic fundraising this fall.
The McCain campaign said the event will be held at the senator's home because it is more private.
But the Phoenix Business Journal said the event was moved from the Phoenix Convention Center due to lackluster ticket sales and concern over anti-war protesters. A McCain aide denied the report on poor ticket sales.
The aide also said the event wasn't moved to McCain's private residence to avoid having the senator and unpopular president appear together on camera.
"We have a policy that fundraising events are closed events," the aide said, adding that any confusion about the fundraiser originally being open to the press should be chalked up to the campaign "working out the kinks" on its first event with Bush.
McCain consistently has trailed the two remaining Democratic presidential candidates in fundraising. The $17 million McCain raised in April was dwarfed by the nearly $31 million by Obama and the $21 million by Sen. Hillary Clinton.
McCain also trails both Democrats in the amount of cash on hand. He had nearly $22 million in the bank at the end of April, while Obama had more than double that amount -- nearly $47 million -- and Clinton had nearly $30 million.
CNN's Alexander Marquardt, Ed Henry, Mary Snow and Robert Yoon contributed to this report.