WASHINGTON -- Republican challenger Mitt Romney, slipping in the polls in critical battleground states, opens an intense campaign focus in three of them Sunday with a rally in Colorado, before heading to Ohio for a three-day bus tour and ending with a stop in Virginia.

President Barack Obama, who was not campaigning Sunday, won all three of those states in the 2008 election that swept him into the White House.

With about six weeks remaining before the Nov. 6 election, the handful of so-called swing or battleground states appear likely to determine the outcome of what has been an extremely close contest between Obama and Romney. Those states become even more critical to the Republican candidate as recent polling shows Obama opening a lead in many of them.

The U.S. president is not chosen by the nationwide popular vote but in state-by-state contests. While most states reliably vote for the candidate of one party or the other, swing states like Colorado, Ohio, Virginia and five others are seen as toss-ups.

Obama enters the weekend with polls showing him in a near tie with Romney nationally. But a new Wall Street Journal/NBC News/Marist Poll shows the president with leads among likely voters of 8 percentage points in Iowa and 5 points each in Colorado and Wisconsin, all battleground states. Polls published earlier this week pointed to leads for Obama in Virginia and Ohio. While he and Romney are neck-and-neck in North Carolina, Obama has an edge in Florida and New Hampshire.

With those factors pressing hard on Romney, he is intensifying his swing-state campaigning to counter criticism from Republican heavyweights that his bid for the nation's highest office is mismanaged and misdirected.

"The Romney campaign has to get turned around. This week I called it incompetent, but only because I was being polite. I really meant 'rolling calamity,"' Wall Street Journal columnist Peggy Noonan, a former speechwriter for President Ronald Reagan, wrote late last week.

Romney's evening rally at a Denver-area high school represents his first public event of the weekend. As the November vote draws near, he also is facing pressure to spend less time raising money and more time explaining his plans to voters in swing states.

The schedule shift comes in the last full week before the presidential debates move the campaign into a new phase -- one which Romney advisers suggest could prove pivotal following several weeks marked by negative attention, missteps and Republican concerns.

Already facing reports of internal finger-pointing and foreign policy questions, Romney suffered another setback last week when a secretly recorded video at a Florida fundraiser for rich donors surfaced showing the Republican standard bearer declaring that almost half of Americans are dependent upon government and see themselves as victims.

Romney's allies worked to reframe the video as an opportunity to draw a contrast between the level of government dependency that Romney and Obama envision.

"I think we had a good week last week," Republican National Committee Chairman Reince Priebus said Sunday on ABC TV's "This Week." "We were able to frame up the debate last week in the sense of what future do we want and do you want out there for your kids and grandkids?"

On Friday, Romney released his 2011 tax returns showing income of $13.7 million, largely from investment income. He paid federal income tax at a 14.1 per cent rate, lower than that of most middle-income Americans. That feeds on the Obama message that Romney is among America's super-wealthy and out of touch with the concerns of average voters.

In an interview set to air Sunday night, Romney told CBS television his campaign is moving in the right direction.

"It doesn't need a turnaround. We've got a campaign which is tied with an incumbent president to the United States," Romney says, according to remarks released in advance by CBS.

Romney spent much of his weekend in high-dollar fundraisers in southern California, a state that has gone Democratic in the last five presidential elections.

As the Republican courted wealthy donors at the Beverly Hills Hilton on Saturday, Obama worked to squash Republican hopes for a resurgence in Wisconsin, where the president assailed Romney's economic approach before an energized gathering of 18,000 in Milwaukee, Obama's biggest crowd of the campaign.

Obama faulted Romney for advancing a top-down economic approach that "never works."

"The country doesn't succeed when only the folks at the very top are doing well," Obama told the massive crowd. "We succeed when the middle class is doing well."