Obama's tax rate in 2010 was about 26 percent. Most of his family's income is from wages and book sale earnings. In 2011, the president and first lady Michelle Obama reported a joint adjusted gross income of $789,674. The couple paid $162,074 in federal taxes, or just over 20.5 percent.
Obama and Democrats have tried hard to paint Romney as a rich, cloistered executive who has little understanding of the less wealthy.
Romney, the son of a former Michigan governor and auto executive, has helped reinforce that impression, talking on the campaign trail about his wife's two Cadillacs and his friendship with NACAR owners.
"We're going to keep pushing this issue all year long," promises Sen. Charles Schumer of New York, the Senate's third-ranking Democrat.
Go ahead, say Republicans, who eagerly counter the Democrats' arguments.
"These new taxes don't lift anybody up, but they do tear some people down," said Senate Minority Whip Jon Kyl, R-Ariz.
Sen. Marco Rubio, R-Fla., said: "This has nothing to do with putting millions of unemployed Americans back to work and everything to do with the president keeping his job. It has nothing to do with sound economic policy and everything to do with class-warfare politics."
Republicans feel they "own" the tax issue politically, ever since Ronald Reagan won the presidency in 1980 with a pledge to dramatically reduce taxes. Within months of his 1981 inauguration, income tax rates were lowered 25 percent over three years.
"They firmly believe in lower taxes. That's their ideology," Steven Greene, an associate professor of political science at North Carolina State University, said of Republicans. Romney has proposed a 20 percent across-the-board cut in marginal income tax rates.
Trying to judge how this issue will play in the election campaign six months from now is tough. But Erickson offers this clue from a survey, conducted for Third Way, of 1,000 independents in 12 battleground states from March 8-18.
It found that 38 percent still making up their minds.
"The standard Democratic message of fairness just won't work with them," Erickson said the poll found, because these voters prefer "an optimistic, opportunity framework on the economy over one based on fairness and income inequality." Fifty-one percent preferred the "opportunity" message, compared with 43 percent who wanted fairness.
"Taxing the wealthy," said Erickson, "is just not their first priority."
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