It could all boil down to Ohio and Florida.
The two states are the sparkling jewels in the swing-state crown. One or the other — or both — could easily end up deciding the Electoral College winner.
Until recently, both states had been leaning Republican, although President Barack Obama carried them in 2008 — Ohio by five points, Florida by three.
No Republican has ever won the presidency without carrying Ohio.
While Obama headed to New York Monday for the U.N. General Assembly, Romney campaigned in Colorado and planned to join running mate Paul Ryan on Tuesday for the last two days of a three-day Ohio bus tour. Obama campaigns in Ohio Wednesday.
Both candidates crisscrossed Florida last week.
Of the 270 electoral votes needed to win the White House, Florida holds 29 and Ohio 18.
Six weeks out, many major polls show a slight Obama advantage, nationally as well as in Florida, Ohio and several other battleground states.
The president's campaign opened a new ad offensive Monday in Ohio with a television spot blasting Romney's remark at a private fundraiser that "47 percent" of Americans don't pay federal income taxes and expect support from the government.
The ad suggests Romney hasn't "come clean" on his own taxes by still refusing to release returns before 2010.
The Romneys did release their 2011 returns Friday, showing they paid a rate of just 14.1 percent on $13.7 million in income. That's below the rate paid by millions of middle-class wage earners.
Romney put out his own swing-state commercial blaming an alleged lax stance by Obama toward China for the loss of U.S. manufacturing jobs.
Romney acknowledged Sunday he was trailing the president in several key states, but said of the polls: "I know that in the coming six weeks, they're very unlikely to stay where they are today."
Follow Tom Raum on Twitter: http://www.twitter.com/tomraum. For more AP political coverage, look for the 2012 Presidential Race in AP Mobile's Big Stories section. Also follow https://twitter.com/APcampaign and AP journalists covering the campaign: https://twitter.com/AP/ap-campaign-2012