U.S. President Barack Obama is crisscrossing the nation on a marathon campaign tour Thursday, while Republican presidential candidate Mitt Romney is concentrating his campaign efforts on the swing state of Ohio.

Mr. Obama has stops planned in the U.S. states of Florida, Virginia, Illinois, and Ohio Thursday. In Illinois, he will cast his ballot for this year's election, taking advantage of his home state's early-voting policy. The other three stops are for campaigning, among voters who could potentially decide the outcome of the presidential election. He returns to Washington late Thursday evening.

Mr. Romney, on the other hand, will remain in Ohio all day, visiting the cities of Cincinnati, Worthington, and Defiance to hold campaign events.

Mr. Obama appeared on a late-night talk show Wednesday to pitch his campaign promises. He vowed to “pull an all-nighter” in the campaign tour that began early Wednesday.

He also referred to controversial remarks about rape and abortion made by a Republican Senate candidate, saying the remarks by Indiana's Richard Mourdock are “exactly why” politicians should not make decisions about women's health care.

Mourdock said he does not believe abortion should be allowed in cases of rape and that pregnancies resulting from rape are “something God intended to happen.” But Mr. Romney's campaign says he has not withdrawn his support for Mourdock, although he disagrees with Mourdock's position.

The states that Mr. Obama and Mr. Romney are visiting Thursday could prove crucial in determining who is assigned the 270 electoral votes needed to win the White House. Mr. Romney's visit to Ohio underscores the historical fact that no Republican has won the White House without winning that midwestern state.

With voter opinion polls showing both men in a virtual tie heading into the November 6 election, the Democratic incumbent and the Republican former Massachusetts governor are making a final push to attract remaining undecided voters.