McCain appeared at a Phoenix high school for the endorsement of Daddy Yankee, a Puerto Rican raggae music icon, as Democrats were opening their national convention in Denver.
"This is a tough presidential campaign we're in," McCain said. "I have a very honorable opponent. There are stark differences between us."
McCain started a busy week, seeking to grab a slice of media attention from Obama who will claim his party's nomination. McCain appeared at the Phoenix high school where his wife, Cindy, graduated, to give a brief talk and accept his new endorsement.
"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.
Yankee was giving the 71-year-old McCain a generational boost, exciting squealing high school students as he offered his endorsement.
"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."
McCain also is scheduled to travel to California to raise money and make an appearance on NBC's "Tonight" show before returning to Phoenix late Monday.
McCain was out of the public eye on Sunday, going to church and a baseball game before a one-hour private meeting at a Phoenix hotel, which aides described as private. They declined to identify those attending. That fueled speculation about McCain's selection of a running mate, a decision he's scheduled to announce on Friday.