Mitt Romney released 23 years of tax returns to Sen. John McCain during the 2008 campaign when he was being vetted as a potential running mate for the Arizona Republican.

Now, McCain – a top backer of Romney’s 2012 presidential bid – says there’s no need for the former Massachusetts governor to release those returns to the general public.

Giving his support to the former Massachusetts governor, Sen. John McCain (R-Ariz.) appears with Republican presidential candidate Mitt Romney at Manchester Central High School in New Hampshire, in January. ) (Melina Mara/THE WASHINGTON POST)

When Schieffer pointed out that Romney gave his returns to McCain’s vetting team four years ago, McCain noted that “we agreed with everybody we considered that that would remain confidential.”

“John Kerry only introduced two years; Mitt Romney did; I did. Two years is sufficient,” McCain continued. “And frankly, I’m not sure that’s the key issue that Americans are really worried about.”

The Obama campaign has pressed Romney to release all of his tax returns. In an interview with Bloomberg TV that aired over the weekend, Obama adviser David Plouffe argued that “If he’s got nothing to hide, then there’s nothing to lose.”

“We know that Governor Romney gave the McCain campaign, when he was considered as a vice presidential candidate, 23 years,” Plouffe said. “So they’re just sitting somewhere in a box or a vault or something, and they ought to release it, because obviously he’s released, you know, a year when he was preparing to run for office.”

McCain, who endorsed Romney ahead of January’s New Hampshire primary, also contended on Sunday that the White House is “demagoguing the Buffett Rule,” Obama’s proposal that the wealthy pay a minimum 30 percent income tax rate.

Rather than focus on the Buffett Rule, McCain argued, the White House should be promoting the bipartisan debt-reduction plan of the Simpson-Bowles commission – a proposal that most congressional Republicans over the past year have rejected as a net increase in taxes.

“We all know that if you’re really serious, if you are really serious about fixing this economy, you’d say, ‘Okay, here’s the Simpson-Bowles Commission. I’m prepared to fix the tax code, clean it up and give the people a few deductions.’ Then you wouldn’t have to worry about rich people paying less taxes,” McCain said.