Gov. Martin O'Malley, President Obama's go-to surrogate during the summer election season, slammed Republican candidate Mitt Romney Sunday morning on Medicare and taxes during an appearance on NBC's Meet the Press.

The Maryland Democrat squared off against a familiar foil, Republican Virginia Gov. Bob McDonnell, as the two presented the talking points for their respective presidential candidates during a quarter-hour segment hosted by David Gregory.

O'Malley, chairman of the Democratic Governors Association, labeled Romney's choice for vice president, Wisconsin Rep. Paul Ryan, as "the leader of the Tea Party Republican Congress" and said the party tickets present a clear choice for the American people.

McDonnell, who heads the Republican Governors Association, responded that this year's contest is a "serious election and it calls or serious candidates who have real solutions."

When asked about Vice President Joe Biden's comment last week that Romney's financial regulation policies would let Wall Street put Americans "in chains," O'Malley offered a tepid defense. Saying Biden made an "indelicate choice of words," O'Malley denied that Biden's words carried a racial message.

"There's not a racist bone in Joe Biden's body," O'Malley said. He then pivoted to an attack on Romney for running "false attack ads on welfare reform." 

But McDonnell had the advantage of a clip that Gregory played of former Virginia Gov. L. Douglas Wilder, an African-American Democrat, criticizing Biden for bringing race into the campaign. "I agree with Gov. Wilder," McDonnell said, calling Biden's comment "over the top."

The Meet the Press segent showed that the issue of Romney's refusal to release more than two years of tax returns still isn't going away. McDonnell insisted the election is "not about Mitt Romney's tax returns."

"He's made a lot of money. He's been successful. He's been a very generous guy," the Virginia governor said.

But OMalley wouldn't let up, saying voters know Romney has engaged in various "tax avoidance schemes" and has been putting his money in offshore accounts and 'betting against the future of the United States."

On Medicare, O'Malley said, "the differences really go to the heart of the country we want to become." He charged that the Medicare changes called for in Ryan's proposed budget would force seniors to pay more for coverage under a voucher-based system.

McDonnell countered that Romney and Ryan are proposing reforms that will give future Medicare recipients more choices.

"Do we not trust people to make good decisions for their own health care?" McDonnell said.

Whether either governor made much of a difference for their presidential standard-bearers is questionable, but there is little doubt that both men succeeded in further raising their national profiles for future elections. One safe bet is that we'll be seeing O'Malley and McDonnell squaring off on Sunday morning news shows again. And again. And again.