COUNCIL BLUFFS, Iowa - One day after President Obama delivered what was by all accounts a lackluster debate performance, Vice President Joe Biden went on the attack against Mitt Romney, delivering zinger after zinger against the GOP nominee and his running mate, Rep. Paul Ryan.

Biden drilled into the former Massachusetts governor on Medicare, saying the governor has changed his position on Medicare so many times that the "public is gonna have collective amnesia" if it believes Romney over "those of us who spent our entire careers protecting and fighting for Medicare."

"Now, they've got a new plan. They've got a lot of new plans. Matter of fact, it's hard to … keep up. It really is hard to keep up," Biden said at the Mid America Center, adding, "I think it's even hard for them to keep up."

The vice president highlighted the lack of detail in Romney's debate answers, saying, "It's bad enough that Gov. Romney won't release the details of his tax returns. Now he won't even release the details of what he plans on doing about your taxes. Seriously. last night the governor walked away from the centerpiece of his economic plan."

Speaking to reporters outside a grocery store, Biden criticized Romney for denying that his tax plan amounted to a $5 trillion dollar tax cut, a charge Obama levied against his GOP rival multiple times during Wednesday's debate.

"Last night, we found out he doesn't have a $5 trillion dollar tax cut, and I guess he outsourced that to China or something. I don't know if that's offshored," Biden said outside a Hy-Vee in Council Bluffs. "But it's hard to figure out what Gov. Romney's position is on a number of issues."

The vice president prodded at Romney for his proposed 20 percent across-the-board tax cut, saying the public realizes the middle class will end up paying for any tax cuts for the wealthy.

"Now folks, I went to a school, a high school that demanded an awful lot of - you had to take math every year. … I'm not a bad mathematician, but I can still add and subtract," Biden said. "Folks, that adds up - what I just said to you - over $5 trillion right there, and that doesn't even count their insistence on continuing the Bush tax cut for the very wealthy, which is due to expire on Jan. 1 of this year, which costs $1 trillion. So now you're over $6 trillion."

The $5 trillion figure that Biden and Obama often cite comes from an analysis of Romney's tax plan conducted by the nonpartisan Tax Policy Center and does include continuing the Bush tax cuts. Romney has insisted that his plan will not add to the deficit and will be entirely paid for. The GOP nominee has yet to specify exactly how he plans to pay for his proposed tax cuts.

"Look, folks, I know we all don't have access to Gov. Romney's accountant. I thought last night when he said, 'I'd like to introduce my accountant,' that I'd love to have his accountant," Biden said. "We may not have his accountant, but we understand someone ends up paying for all of this."

But while Biden delivered a handful of zingers against Romney's tax plan, he also provided fodder for Republican attacks against his own. The GOP's rapid response team shot out a clip of Biden's speech in which he said "yes we do" want to raise taxes by a trillion dollars. The clip cut out Biden's next words - "in one regard" - in which he explained that those trillion dollars would come only from the "superwealthy."

"On top of the trillion dollars of spending we've already cut, we're going to ask - yes, we're going to ask the wealthy to pay more," Biden said. "You know the phrase they always use. 'Obama and Biden want to raise taxes by a trillion dollars.'Guess what? Yes, we do, in one regard. We want to let that trillion-dollar tax cut expire so the middle class doesn't have to bear the burden of all that money going to the superwealthy. That's not a tax raise. Tthat's called fairness where I come from."

Romney spokesman Ryan Williams said shortly after Biden's remarks that they showed Biden had "fully embraced the president's job-killing tax increases."

"Fresh off admitting that America's middle class has been 'buried' over the last four years, Vice President Biden went a step further today and fully embraced the president's job-killing tax increases," Williams said. "The choice facing Americans in this election gets clearer every day."

Obama campaign spokeswoman Lis Smith responded on Twitter, saying the GOP was attacking Biden "for siding with a majority of Americans and wanting a balanced approach to deficit reduction."

Biden said he spoke to President Obama before his debate performance. The vice president lauded his boss for staying consistent and took a not-so-subtle dig at Romney for not doing the same.

"I learned this man never says anything he doesn't mean, and means what he says," Biden said of Obama. "He never, never says - unlike some others, he never says one thing one day, another thing the next day, and he never changes position because it may be politically convenient."