West Palm Beach, Fla. ? On a day that combined two campaigns into one, President Barack Obama on Wednesday challenged Republicans to raise taxes on the rich as GOP rivals Mitt Romney and Newt Gingrich swiped at him on the economy and criticized each other over immigration.

With a week to go before the Jan. 31 Florida Republican presidential primary, the polls suggested a tight race, although Romney and his allies seized a staggering advantage in the television ad wars. They have reported spending $14 million combined on commercials, many of them critical of Gingrich, and a total at least seven times bigger that the investment made by the former House speaker and an organization supporting him.

Obama’s political timeline was a different one, Election Day on Nov. 6. In a campaign-style appearance in Iowa, he demanded Congress approve a tax increase for anyone like Romney whose income exceeds $1 million a year.

“If you make more than a million dollars a year, you should pay a tax rate of at least 30 percent. If, on the other hand, you make less than $250,000, which includes 98 percent of you, your taxes shouldn’t go up,” he said after touring a manufacturing plant in Cedar Rapids and in a state that he won in 2008 that was expected to be a battleground in the fall.

“This is not class warfare,” he said. “That’s common sense.”

As Obama surely knew, it was an offer Gingrich, Romney and the anti-tax Republicans in Congress are likely to find easy to refuse.

Referring to Obama’s call in the speech for Congress to end tax breaks that encourage companies to ship jobs overseas, Romney said he didn’t know of any.

Instead, he said the president presides over “the most anti-business, anti-investment, anti-job creator administration I’ve ever seen, and so, what I’ll do — I’ll get America to work again. I spent 25 years in business.”

Gingrich was far harsher at an appearance in Miami.

“If he actually meant what he said it would be a disaster of the first order,” Gingrich said of the president’s call for higher taxes on millionaires.

The former House speaker said the president’s proposal would double the capital gains tax and “lead to a dramatic decline in the stock market, which would affect every pension fund in the United States.”

“It would affect every person who has a 401(k). It would attack the creation of jobs and drive capital outside of the United States. It would force people to invest overseas. It would be the most anti-jobs single step he could take,” he said.

Under current law, investment income is taxed as the rate of 15 percent, a fact that has come to the fore of the campaign in recent days with the release of Romney’s income tax return.

Wages, by contrast, are taxed at rates that can exceed 30 percent.

Electability is the top concern for GOP primary voters, according to polls taken in the early primary and caucus states, so both Republicans were eager to paint a contrast with the president.