WASHINGTON -- Presumptive vice presidential nominee Paul Ryan said on Sunday that while he turned over "several years" of tax returns to the Romney campaign during his vetting process, he would only make two years of tax returns public for voters.

The Wisconsin Republican, appearing alongside Romney on "60 Minutes" for their first joint media interview, seemed poised and assured throughout the 15-minute segment. When pressed with a question about tax returns -- a topic that has dogged Romney -- Ryan had a ready answer.

"It was a very exhaustive vetting process," he told CBS's Bob Schiefer. "It is a confidential vetting process. So there were several years. But I'm going to release the same amount of years that Governor Romney has. But I got to tell you Bob -- two, I'm going to be releasing two, which is what he's releasing -- what I hear from people around this country, they are not asking, 'Where are the tax returns,' they are asking where the jobs are? Where is the economic growth?"

Romney, in fact, has not yet released two years of tax returns. He released his 2010 return (with some elements missing) and an estimate for 2011. The campaign has said that a full 2011 return will be made public before the election.

The issue of tax fairness dominated the 60 Minutes interview with Schiefer repeatedly questioning whether a Romney-Ryan administration would level the progressivity of the tax code. While the CBS host never mentioned it, under Ryan's proposed budget, Romney would have paid an effective tax rate of 0.82 percent in 2010, according to the Atlantic.

For his part, Romney insisted he would continue to require the wealthy to pick up the heaviest burden.

"Fairness dictates that the highest-income people should pay the greatest share of taxes, and they do," Romney said. "And the commitment that I've made is we will not have the top income earners in this country pay a smaller share of the tax burden. The highest-income people will continue to pay the largest share of the tax burden and middle-income taxpayers, under my plan, get a break. Their taxes come down."

At one point, Ryan interrupted the man who had just made him the presumptive vice presidential nominee. "What we are saying is: Take away the tax shelters that are uniquely enjoyed by people in the top tax brackets," he said, "so they can't shelter as much money from taxation, so that you can lower tax rates for everybody to make America more competitive."

It was a fairly straightforward overview of tax reform: Eliminate the loopholes and use those savings to lower rates across the board. But it was also a bit awkward. Just last week, new questions were raised over the role Romney played in using the tax shelter Son of Boss while heading up the audit committee of the Marriott hotel empire in the 1990s.

Democrats quickly seized on the tax return question. Danny Kanner, a spokesman for the Obama campaign, blasted out an email after the interview aired: "If Mitt Romney needed to examine several years of tax returns to determine whether Paul Ryan was qualified to be Vice President, why won't he let the American people see his own returns and determine if he himself is qualified to be President?"