(image: 401k / flickr)

How can you tell when an idea is really popular across the political spectrum? When both the Democratic and Republican candidates for president feel they must give it at least lip service in order to attract voters. So it is with the idea that rich people should pay taxes.

First, on the Democratic side, President Obama:

“You can’t reduce the deficit unless you take a balanced approach that says, ‘We’ve got to make government leaner and more efficient,’” the president told CBS’s Scott Pelley. “But we’ve also got to ask people –like me or Gov. Romney, who have done better than anybody else over the course of the last decade, and whose taxes are just about lower than they’ve been in the last 50 years – to do a little bit more.”

Obama said he would be willing to make “some adjustments to Medicare and Medicaid that would strengthen the programs.” “The way to do that is to keep health care costs low. It’s not to ‘voucherize’ programs so that suddenly seniors are the ones who are finding their expenses much higher.”

That was a reference to Mitt Romney and running mate Paul Ryan. The Republicans have proposed a plan that would transform Medicare by giving the elderly voucher-style payments they could use to purchase health insurance. They say it would rein in runaway health care costs. But Democrats — and the impartial Congressional Budget Office — say it would eventually shift much of the burden of health care costs to the elderly.

Even as Romney’s surrogates responded with a blistering reply, Romney himself was stating something that would have been unthinkable for him as recently as a month ago — namely, the notion that rich people should pay taxes:

Mitt Romney rejected claims by President Barack Obama that he would sign off on more tax breaks for the wealthy if elected president, but again declined to offer specifics on how exactly he would accomplish his goal of lowering taxes for other Americans while also balancing the budget.

In an interview with NBC’s “Meet the Press,” Romney said he would offset his proposed 20 percent tax cut for all Americans by eliminating loopholes and deductions for high-income earners. He argued that his plan would in effect lower taxes for middle class Americans while keeping tax rates the same for wealthy Americans.

“People at the high end, high income taxpayers, are going to have fewer deductions and exemptions. Those numbers are going to come down. Otherwise they’d get a tax break,” Romney told NBC. “And I want to make sure people understand, despite what the Democrats said at their convention, I am not reducing taxes on high income taxpayers.”

This tells me two things: First, that Romney knows he can’t win from the Republican base alone. Second, that making rich people pay taxes is so universally popular that Romney feels he must blow off a huge chunk of his base in order to chase general-elections voters who like the idea of the rich paying taxes. Hoocouldanode?