"Barack Obama has failed America," Romney said at a chili cookout on a 300-acre farm owned by former New Hampshire House Speaker Doug Scamman and his wife, Stella.
When Obama ran for president, "we didn't know what sort of a president he would make," Romney, 64, said in prepared remarks. "It was a moment of crisis for our economy, and when Barack Obama came to office, we wished him well and hoped for the best. Now, in the third year of his four-year term, we have more than promises and slogans to go by."
If elected, from his "first day in office," Romney's "No. 1 job" would be "to see that America once again is No. 1 in job creation," the candidate said on Bittersweet Farm, whose 300 acres were preserved in part with $1 million in federal money, a report in Seacoast Online indicated.
A Romney White House would also "return responsibility and authority to the states for dozens of government programs -- and that begins with a complete repeal of Obamacare," Romney said, using a pejorative nickname for Obama's healthcare reforms.
Moments before Romney made his declaration, former Alaska Gov. Sarah Palin -- the subject of speculation about her presidential interests -- attacked Romney on a healthcare plan similar to Obama's that he pushed through as governor.
Romney's plan provided near-universal health insurance access through subsidies and state-level mandates.
Speaking near Boston's Bunker Hill, the site of a famous U.S. Revolutionary War battle, Palin said, "In my opinion, any mandate coming from government is not a good thing."
"Even on a state level and even a local level, mandates coming from a governing body, it's tough for a lot of us independent Americans to accept, because we have great faith in the private sectors and our own families, and our own businessmen and women making decisions for ourselves," she told reporters.
She said Romney would have a "big challenge" appealing to the populist conservative and libertarian Tea Party movement.
Her East Coast bus tour then headed to New Hampshire for a clambake in the coastal town of Portsmouth.
Former Utah Gov. Jon Huntsman was to arrive in New Hampshire this weekend. Former Minnesota Gov. Tim Pawlenty has said he will compete aggressively in New Hampshire too.