"Can I give you a little straight talk?" the Arizona senator said, using his trademark expression at the end of one of his trademark town-hall meetings. "The state of New Hampshire will be a battleground state. I intend to be back and back and back."
He also used the visit, little more a week after he officially won enough delegates to be the nominee, to publicly make peace with some of his primary rivals. He singled out
"We are reuniting our party and we've got to re-energize it," he told a crowd of several hundred.
Earlier in the day, McCain told reporters he had begun to flesh out his plans for conducting the search for a running mate, but he also declared the process too fresh to begin ruling in or out any candidate.
Of Romney, who on Tuesday said he would accept an offer, McCain told the town-hall audience: "He fought hard, he fought well. I believe that Governor Romney has earned a place in our Republican Party and I think he's part of the future of our Republican Party."
The senator called Giuliani "a genuine American hero" for his leadership following the 9/11 terrorist attack, and Huckabee and Thompson good and decent men.
McCain was accompanied by Connecticut Sen. Joe Lieberman, an independent, who also has been mentioned as possible running mate, as he was in 2000 when he was the Democratic vice presidential nominee.
Lieberman jabbed at Democrats Hillary Rodham Clinton and Barack Obama, who have been jousting over experience by debating who is best equipped to answer a crisis call in the middle of the night.
Lieberman said of McCain: "He's ready to be commander in chief not just at 3 a.m. - but at any a.m. or p.m., 24/7. This guy knows what it means to be a leader."
McCain had been the Republican front-runner before overspending and mismanagement left his campaign on the verge of extinction last July.
He scaled back his operation, emphasized his town meetings and ended up winning the New Hampshire primary with 37 percent of the vote. Romney finished second with 32 percent, while Huckabee trailed at 11 percent and Giuliani at 9 percent.
McCain's visit on Wednesday came amid a nationwide fundraising swing that included stops in New York on Tuesday, Boston on Wednesday, Philadelphia on Thursday and Chicago on Friday.
The senator canceled a planned visit to Harrisburg, Pa., on Thursday morning to participate in Senate votes on a signature issue: legislation placing a one-year moratorium on earmarked projects by members of Congress.
He reached out to his Granite State audience with a plea to preserve the state's first-in-the-nation primary, not just because he won it amid a failed campaign in 2000 and his successful campaign this year.
He said Iowa, New Hampshire and South Carolina should be first in the nominating process, because their voters have proven that they pay close attention to the candidates, and then both parties should work on a bipartisan plan for contests in different regions of the country.
"There ought to be a way to work this out," he said.
He also said he wanted the Republican National Committee to seat all of New Hampshire's convention delegates amid a proposed party penalty after the state moved up its primary date to Jan. 8.
"I want 'em seated," McCain said of the delegates. "I think they were driven by circumstances beyond their control, in that all the other states were moving their primary earlier."
Following his town-hall meeting, McCain made an impromptu stop at the Pease International Tradeport in Portsmouth, where a group of armed services members were deploying to the Middle East for training before an upcoming deployment to Iraq and Afghanistan.
Standing atop a baggage conveyor in an otherwise empty terminal, the Vietnam War veteran told the group: "Thank you for serving our country. You're the best of America."