Obama in Colorado ahead of Democratic Convention

President Barack Obama cranked up campaigning on his road to the Democratic National Convention in the swing state of Colorado on Sunday, as top aides slammed his Republican opponent.

With the election barely nine weeks away, Obama is locked in a tight contest against Mitt Romney, whose campaign has doggedly stood its ground and even upstaged the slick fundraising that swept the incumbent to power in 2008.

The current campaign has been a grinding battle so far for the president: the euphoria of four years ago is a fading memory and Obama will use the Democratic National Convention, starting Tuesday, to seek a fresh mandate.

Obama's current tour of battleground states, dubbed the "Road to Charlotte," in reference to the city in North Carolina where the convention takes place, has underlined the closeness of the race.

His bid for a second White House term hinges on a handful of swing states but the convention is a four-day opportunity for Democrats to dominate the political conversation despite the backdrop of a bumpy U.S. economic recovery.

Obama's supporters will aim to counter Republican claims that, though his 2008 election win was historic, his presidency is a bust.

Obama is in Boulder, Colorado and was due to speak at an event around 1pm (1900 GMT).

In Iowa on Saturday, Obama mocked the discussions at last week's Republican National Convention in Tampa, Florida for promoting a policy agenda dating from the "last century" that was heavy on rhetoric but light on substance.

"It was a rerun. We've seen it before. You might as well have watched it on a black and white TV," Obama joked to supporters in Urbandale.

With the main events broadcast in prime time, the U.S. conventions are a rare opportunity to enter voters' living rooms and, though viewing numbers are on a path of decline, the events remain a mainstay of election season.

Obama will speak in Charlotte on Thursday, when he will also receive the party's official nod to take on Romney, paving the way for a two-month run-in to the November 6 national vote.

Nearly four years after inheriting a nation beset by a financial crisis that occurred under his Republican predecessor George W. Bush, Obama still faces a divided electorate looking for a way out of shaky economic times.

Romney, a former venture capitalist and ex-governor of Massachusetts, used last week's Republican convention to urge voters to give him the chance to turn around the nation's fortunes.

Romney has trailed Obama for much of the race and still lags in swing states such as Florida, Ohio and Pennsylvania, but the Republican's campaign is well-financed and has raised tens of millions more than the president.

Romney's most consistent charge is that Obama, despite vowing to reverse the rise of the oceans and heal the planet, has simply not delivered what Americans care most about: economic prosperity.

"You know there's something wrong with the kind of job he's done as president when the best feeling you had was the day you voted for him," Romney said last week.

Despite the economy – U.S. unemployment stands at 8.3 percent and 62 percent of voters in a recent CBS poll said they believed their country is heading in the wrong direction -- Obama goes into his convention with key advantages.

He leads or ties Romney in polls of national public opinion and he has multiple and easier paths than his rival through the battleground states that will decide the election.

Obama is also seen as more likable, stronger on foreign policy and more sympathetic to the middle class than his Republican rival.

But the convention in Charlotte is his biggest week on the campaign so far, and it attracts risk as well as possible electoral reward.

On Sunday, one of the president's top strategists, David Plouffe, set the likely tone for the week, telling ABC's "This Week" program that Republicans, if elected, would jeopardize the economy.

"We're going to explain to the American people and the middle class of this country how we're going to continue to recover," said Plouffe.

"If we take Mitt Romney's path, economists have looked at this, the recovery would slow down, we wouldn't produce jobs -- he would give huge tax cuts to people like himself and send a bill to the middle class and seniors."