Mitt Romney vows to oust Obama after primary sweep
Republican presidential hopeful Mitt Romney has vowed to take the White House from President Barack Obama and end four years of "disappointments".
Speaking while racking up a series of primary night victories, he said a "new campaign" was beginning, heralding the start of the road to November's vote.
"Hold on a little longer. A better America begins tonight," he said.
The presumptive nominee easily won primaries in Connecticut, Delaware, New York, Pennsylvania and Rhode Island.
His claim to the Republican nomination is now unrivalled, with no serious challengers remaining in the contest.
With 14 primaries remaining , Mr Romney has amassed an unbeatable lead in the race for the delegates who will formally crown him the Republican nominee at the party's convention in late August.
Without competition in the remaining contests he is expected to cruise past the 1,144 delegates he needs to take the nomination.
Among the states still to vote are California and Texas, both heavily populated states with large hauls of delegates.
Just Newt Gingrich and Ron Paul actively remain in the contest.
Mr Gingrich, a former speaker of the House of Representatives, spoke in North Carolina as Tuesday's results came in but gave few clues as to his future in the contest.
He had pinned his hopes on a strong showing in Delaware, but instead polled less than half of Mr Romney's total.
'We're not stupid'
As the results began to come in on a night with the most electoral delegates at stake since Super Tuesday, Mr Romney took the stage in New Hampshire, the site of his first primary win of the year.
He focused on the forthcoming general election campaign, saying America needed a new direction and a renewal of its greatness.
"Tonight is the start of a new campaign to unite every American who knows in their heart that we can do better," he said.
"The last few years have been the best that Barack Obama can do, but it's not the best America can do.
"Tonight is the beginning of the end of the disappointments of the Obama years and the start of a new and better chapter that we will write together."
He accused the president of failing to deliver on his promises of "hope and change" made during his 2008 election campaign.
The average American is still feeling the pain of the economic collapse, Mr Romney said. "It's still about the economy… and we're not stupid."
Shortly after Mr Romney's remarks, Mr Obama took to the stage in Colorado, a state his strategists see as part of a potential route to re-election.
Mr Obama is making a three-state tour of campuses in Colorado, North Carolina and Iowa - all swing states set to feature heavily in November.
The trip is an effort to highlight the growing cost of higher education and, analysts say, revitalise his support among young voters who may have become disillusioned with the president since 2008.
He stressed his humble background and said that the election in November would be about making education, and the nation as a whole, affordable for ordinary people.
Obama spokesman Ben LaBolt said in a statement that the choice between the two men was clear.
"The title for Governor Romney's speech tonight should have been Back to the Future, because he has proposed a return to the same policies that got us into the economic crisis in the first place," he said.
"Mitt Romney has spent the past year out on the campaign trail tearing down the president with a negative message that even Republicans who have endorsed him have criticised.
"This marks the end of that monologue. Now he must put his record and his agenda next to the president's."