The Arizona senator, in a campaign appearance in Norfolk, Va., also called on conservatives, who have been wary of some of his positions, to support him, The Virginian-Pilot reported.
"The best way of succeeding is a united party," McCain said. "We need to re-energize our base."
McCain,a former Navy pilot and prisoner of war in Vietnam, emerged as the GOP front-runner this week after winning primary victories Tuesday. Further cementing his status was former Massachusetts Gov. Mitt Romney's decision later in the week to suspend his campaign.
"He's the only person who can be commander in chief on day one," Lehman said of McCain.