With Election Day less than two weeks away, President Obama launched a campaign blitz across battleground states Wednesday to sway remaining undecided voters and rally his Democratic base, while Republican challenger Mitt Romney urged Americans not to settle for “more of the same.”

Campaign officials said Obama’s exhausting jaunt across eight states, intended to save a historic presidency that began with great promise but now is potentially imperiled by Romney’s challenge, has been in the works for weeks. The president is flying coast to coast, visiting six battlegrounds: Iowa, Colorado and Nevada on Wednesday and then Florida, Virginia and Ohio on Thursday. All are states critical to his reelection prospects. Obama is also stopping in California on Wednesday to appear on “The Tonight Show with Jay Leno” and will squeeze in a Thursday trip to his home state of Illinois to become the first sitting president to vote early.

Romney, campaigning in Nevada, told supporters at a rally in Reno that the nation is slipping backward under Obama’s leadership and vowed that Republican policies would get it on track.

“You can boil what he’s saying down to four simple words — more of the same,” Romney said. “And we don’t want more of the same.” He said he and his running mate, Rep. Paul Ryan (Wis.), “have a plan with five simple steps,” which he promised “are going to get America’s economy just cooking again.”

After speaking at a late-night rally in Las Vegas on Wednesday, Obama plans to skip staying at a hotel, instead remaining overnight on Air Force One and flying to Tampa, where he will go directly to his first event on Thursday. From the plane, he will call undecided voters (though presumably not in the middle of the night).

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“We’re doing this now because we feel this is a pivotal time in the election,” Obama campaign spokeswoman Jen Psaki told reporters Wednesday morning aboard Air Force One. She noted that early voting has begun in many states and that in Colorado, one stop on the president’s itinerary, 78 percent of people voted early or by mail in 2008.

Obama is excited about the trip, Psaki added. “We’re all going to be going on adrenaline for the next 36 hours or so, and that’s the fun of it,” she said.

Obama’s campaign has remained confident in the face of polls showing the race in a dead heat and Romney’s momentum in recent weeks, insisting that the president still has more paths to secure an Electoral College majority in the Nov. 6 election.

At his first stop Wednesday morning, a fairgrounds in Davenport, Obama was exuberant and clearly energized by the approaching end of the campaign. Taking the stage to loud cheers from a crowd of 3,500 supporters packed into an open field, he called out the refrain that evoked his epic rallies in 2008: “Hello, Iowa!... Are you fired up? Are you ready to go?”

The crowd roared in the affirmative.

Obama talked about the trip to come. “This is the first stop on our 48-hour fly-around marathon campaign extravaganza,” he said. “We’re going to pull an all-nighter. No sleep.”

Then, he launched into his familiar refrain of the campaign’s final days, tearing into Romney and accusing his opponent of having “Romnesia” for switching his positions and trying to move to the political center. He also talked about proposals for the country’s future that his campaign released Tuesday, called “A Plan for Jobs & Middle-Class Security.” The booklet contains few new proposals, but campaign officials think it will rally their base and get people to the polls.

In excerpts of an interview with the Des Moines Register released Wednesday, Obama went further than the plan, promising to tackle the country’s budget problems head on in the first six months of a second term.

“When you combine the Bush tax cuts expiring, the sequester in place ... we’re going to be in a position where I believe in the first six months we are going to solve that big piece of business,” Obama said.

“It will probably be messy. It won’t be pleasant,” Obama added. “But I am absolutely confident that we can get what is the equivalent of the grand bargain that essentially I’ve been offering to the Republicans for a very long time, which is $2.50 worth of cuts for every dollar in spending, and work to reduce the costs of our health-care programs.”

Obama also said he thought Congress and the White House could “credibly meet” the target that the Bowles-Simpson debt reduction commission set of $4 trillion in deficit reduction.

Later Wednesday, the president brought his marathon swing state tour to a park in the shadow of the Rocky Mountains , telling thousands of raucous Denver supporters that “we cannot go back” to Republican policies that he said created an economic mess.

The Romney campaign immediately responded, saying Obama would lose the state on Nov. 6. “In two weeks, Coloradans will choose Governor Romney’s positive agenda over President Obama’s increasingly desperate attacks,’’ said Amanda Henneberg, a campaign spokeswoman.

Denver resident Juju Nkrumah, 66, who attended the rally, countered that she likes Obama’s chances in the state. “I don’t think Romney is doing better,’’ she said. “In my neighborhood, he’s not doing better.’’

Evoking Romney’s infamous remark at a fundraiser that appeared to dismiss 47 percent of Americans as government freeloaders who see themselves as “victims,” she said: “We are the 47 percent.’’

Renat Farmar, 79, of Denver, said she was cutting Obama some slack because “he cannot change the world in four years. He had a mess when he came into office. How can you create jobs if the companies won’t hire?’’

With his debates with Obama behind him, Romney is trying to build momentum this week around his candidacy, staging large and enthusiastic rallies in Nevada and Colorado before he jets off to the Midwestern battlegrounds of Iowa and Ohio later Wednesday. The Republican nominee, who had lagged behind Obama for months this summer and into the fall, told some 2,500 supporters at a Reno arena that the debates were “propelling” his campaign.

“The president can’t seem to find an agenda to help America’s families,” he said. “Our campaign is a growing movement across this country.”

He described Obama’s booklet of proposals as too little, too late. Obama “doesn’t understand what it takes to get this economy going,” Romney said. “He doesn’t have a plan to get jobs for Americans. I do, and that’s why I’m gonna win.”

Romney tried to paint a portrait of an economically beleaguered nation, talking about people who are struggling to make ends meet yet do not register in government statistics. He recalled meeting a man in his 50s a few days ago who told him the job he used to have paid him $25 an hour plus benefits, but that now he is working for $9 an hour without benefits.

“He said, ‘You know, I’m showing up on the employment rolls, but my life is changed dramatically,’” Romney said.

Of Obama’s campaign slogan, ‘Forward,’ Romney said, “It doesn’t feel like ‘Forward’ to 23 million Americans struggling to get a good job. It doesn’t feel like ‘Forward’ to the millions of people who don’t have as good of a job as they did a few years ago. It doesn’t feel like ‘Forward.’ It feels like ‘Backward.’”

In Nevada, where early voting began this week, polls suggest Romney is trailing Obama. Despite Nevada’s dire economic picture — the state has the nation’s highest unemployment rate, at 11.8 percent — Obama is buoyed by an extensive ground operation, a growing number of Hispanic voters and a powerful organized labor presence.

Romney focused some of his remarks in Reno on Nevada’s depressed housing market, predicting that if Obama is reelected, “I’m convinced you’re going to see the values of your homes continue to bump along in the basement, and you’re going to find it hard to get a mortgage.”

“If I’m elected — when I’m elected — we’re going to do this, we’re going to finally get this housing market going and get jobs and get this economy going,” he said.

Speaking to reporters in Davenport, the Obama campaign’s chief strategist, David Plouffe, exuded confidence about Obama’s position in battleground states. He was asked about the possibility that the Romney camp is bluffing about his strength right now in an effort to build momentum in those battleground states.

Plouffe said he senses that “they are very concerned about Ohio,” and he suggested that Romney’s spending and travel schedule belie his campaign’s narrative that Florida and Virginia “are moving in their direction.”

“I believe they are overstating their electoral college situation,” Plouffe said. The amount of time Romney is spending in Ohio, along with “historic amounts” of spending in Florida and Virginia by the Romney campaign and super PACs, indicate that his handlers may be less confident about their chances in those states than they let on, he said.

For Obama, after Davenport it was back to Air Force One and on to Colorado, the next stop in a campaign swing that could well help determine who the next occupant of the Oval Office will be.

Rucker reported from Reno. Jason Horowitz in Davenport contributed to this report.