President Obama has elevated one question to a key campaign issue -- what is a "fair share" of taxes?
Obama repeatedly invokes tax fairness as a major campaign issue, returning over and over to the phrase "fair share," as he did on June 22 when he talked about a policy "that asks the wealthiest Americans to help pay down our deficit, to do their fair share."
At a May 14 campaign stop, he used similar language, saying the idea is to make "sure that everybody is paying their fair share."
Republicans, however, question the premise.
"You got the top 2 percent paying almost half of all income taxes. Is that fair?" Sen. Jon Kyl, R-Ariz.
Kyl was referring to official figures showing how much various income levels earn of the nation's total income compared to how much they pay of the nation's total income taxes.
IRS figures show the top 1 percent of earners take home 16.9 percent of the nation's total income, but pay 36.7 percent of the nation's income taxes.
The top 5 percent take home a little more than 31 percent of total income but pay almost 59 percent of all income taxes.
And the top 10 percent earn just over 43 percent of the total income but pay more than 70 percent of all income taxes.
"How are you going to make it fairer? If they pay 75 percent?," asks Arthur Brooks of the American Enterprise Institute. "If they pay 90 percent? If they pay all of it? Will that finally be fair?"
As it now stands, 90 percent of all Americans pay only 30 percent of all income taxes.
"If we want an income tax system that is fair according to the Obama administration's own standards, we already have it," Sen. Kyl says. "The argument that top-tier earners are not doing enough just does not hold water."
However, advocates of higher rates for the wealthiest Americas typically argue that it is much easier for those top earners to pay more in taxes, as compared to lower-income Americans who have much less discretionary income.
The president does not mention another factor in the fairness equation -- close to half of American workers pay no federal income taxes at all.
"That's extremely progressive," says Arthur Brooks. "That's more progressive than our European friends, as a matter of fact."
And Kyl notes, "people who do not share in the sacrifice of paying taxes have little direct incentive to care whether the government is spending and taxing too much."
The administration often points to the ultra wealthy who sometimes pay lower rates because they have a lot of deductions. But the averages for all groups paint a more accurate picture.
The top 1 percent, for instance, pay an average tax rate of more than 24 percent. The top 5 percent -- a tax rate of a little more than 20 percent. The top 10 percent -- about 18 percent.
For the bottom 50 percent of taxpayers, the average rate is 1.85 percent.
Though fairness is one of the president's favorite themes, polls suggest voters are not that receptive.
A Democratic think tank polled independents in 12 battleground states and found the president's fairness message does not resonate.
"They don't see themselves as victims in the system, so about 60 percent of them say our system is basically fair," explains Lanae Erickson Hatalsky of the Democratic think tank Third Way. "When you ask them how to grow an economy, they didn't talk about fairness. They talked about opportunity."
"When the president of the United States or any politician basically equates spreading the wealth around with fairness, that's fundamentally at odds with what most Americans think fairness means."
Even Democrats who agree the system is progressive, though, still argue taxes on the wealthy may have to go up.
"We have a country that's aging. We have deficit problems going forward," says Chuck Marr of the Center for Budget and Policy Priorities. "And so in the coming years there's going to be pressure to sort of bring these taxes off the bottom where they are now."
Nevertheless, few dispute the tax system is progressive, or that the wealthy pay what many see as a fair share.
In fact, one recent poll by the newspaper The Hill asked people what the maximum tax rate should be, and 75 percent of them said 30 percent or below. That 30 percent is higher than the 24 percent the top 1 percent is actually paying. But the current top tax bracket carries a 35 percent rate, and the president wants to raise that to almost 40.