Chris Usher/AP Photo; Eric Kayne/Getty Images

Mitt Romney is standing firm on his plans to release two years worth of tax returns and nothing more. Romney already released his tax return for 2010, and an estimate for 2011. When asked for a firm date for the release of the 2011 return, a top Romney adviser said he couldn't provide one.

On Fox News this morning, Romney said, "John McCain ran for president and released two years of tax returns." He added, "John Kerry ran for president and you know his wife who has hundreds of millions of dollars. She never released her tax returns and somehow this wasn't an issue."

The Romney campaign believes the issue of Romney's returns isn't resonating with voters as much as the Obama campaign would like.

Top Romney adviser Kevin Madden tells ABC News the calls will never end for Romney's tax returns. No matter how many years Romney releases, "It won't be enough," Madden said.

While the Romney campaign will not offer a firm date for the release of the 2011 return, Madden indicated that when the return is made public, voters will see Romney actually paid more in taxes than what was in the 2011 estimate already released.

When asked about the juxtaposition of images this weekend, of President Obama on the campaign trail and Romney at his summer home in Wolfeboro, N.H., Madden said, "It is the right time to get him out there more."

Romney will be in the battlegrounds of Pennsylvania and Ohio this week.

In addition to stepping up their attacks on what they call President Obama's cronyism - rewarding wealthy donors and friends - the Romney campaign will also argue this week that this debate over Romney's tax returns and the candidate's role three years after Romney left Bain Capital in 1999 are "distractions" by the Obama campaign. Romney, they say, remains focused on the big issues including the economy and jobs.

Get more pure politics at ABC News.com/Politics and a lighter take on the news at OTUSNews.com