"This is a tough presidential campaign we're in," McCain said. "I have a very honorable opponent. There are stark differences between us."
In recent speeches, McCain has criticized Obama as not ready to be president and as a candidate who is willing to lose the war in Iraq to win the campaign. When Obama charged that McCain was questioning his patriotism, McCain responded that he was only questioning Obama's judgment.
Seeking at least a slice of media attention amid the Democratic National Convention, McCain visited the Phoenix high school where his wife, Cindy, graduated.
"I know you have students who come from all over the world. I know there are people here who come from countries, some from Iraq where they have seen the look of war and sacrifice," he said.
McCain, who turns 72 on Friday, got a generational boost from Daddy Yankee, a Puerto Rican star of reggaeton, a mix of reggae, rap and Latin music styles. Students squealed with delight as Yankee appeared and endorsed McCain.
"I believe in his ideals and his proposals," Yankee said. "He's been a fighter for the Hispanic community. He's been a fighter for the immigration issue."
Later at a fundraiser in Sacramento, Calif., McCain told backers - including Gov. Arnold Schwarzenegger - that he's seeing good news in the polls.
"We had a very good poll today," said McCain, pointing to a Gallup tracking poll showing the race a virtual dead heat .
McCain vowed to put the nation's most populous state in play, though Obama is thought be ahead there.
"We will not take your money and leave," said McCain. "We will compete in California."
He repeated his vow to expand offshore drilling, while noting that Schwarzenegger opposes that drilling.
"I've got to give you straight talk," said McCain. His only reference to Obama came when he charted their differences on Iraq.
McCain was heading to Burbank, Calif. for an appearance on NBC's "Tonight" show.