Paul Ryan says "it would take me too long to go through all the math" involved in the tax plan he and Mitt Romney are proposing.

The Republican vice presidential nominee said on "Fox News Sunday" that their plan--a 20 percent across-the-board income tax cut--would focus on deductions and closing tax loopholes for the rich, but declined to offer specifics.

The Obama campaign seized on Ryan's comments, firing off this response:

Romney has promised $5 trillion in tax cuts skewed toward millionaires and billionaires, but refused to say how he'd pay for them without raising taxes on the middle class or exploding the deficit. He's promised to repeal ObamaCare, but refused to say what he'd replace it with to protect the 129 million Americans with pre-existing conditions. He's promised to repeal Wall Street reform, but refused to say what he'd replace it with so that big banks aren't writing their own rules again.

But New Jersey Gov. Chris Christie defended the pair's tax plan on Sunday's "Meet The Press."

[Related: Chris Christie: Wednesday night's debate is 'the restart of this campaign']

"Governor Romney has a vision for the direction of this country," Christie said. "He's not an accountant. He's not going to go line by line, as much as you'd like him to do, through the budget."

Christie then pivoted to President Obama. "Let's hold the president to the same standard and criticize him as well," Christie said. "How's he going to create a million new manufacturing jobs? He hasn't told anybody the specifics of that. How's he going to reduce $4 trillion in debt? We're still waiting to hear what he thinks about Simpson-Bowles, which he commissioned. I mean, he's been the president, and hasn't given us specifics. So let's be fair here."

Ryan admitted the campaign has made several "missteps," including Mitt Romney's controversial "47 percent" comments about President Obama's core supporters. On Sunday, Ryan called those comments "inarticulate" and lacking "eloquence."

"Mitt acknowledges himself that was an inarticulate way of describing how we're worried that in a stagnant Obama economy more people have become dependent on government because they have no economic opportunity," said Ryan, chairman of the House Budget Committee. "It was an inarticulate way to describe what we're trying to do to create prosperity and upward mobility, and reduce dependency by getting people off welfare back to work."