Updated

DICKSON CITY, Pa. -- Vice President Joe Biden on Monday criticized outside Republican groups for pouring vast sums of unaccounted-for cash into GOP campaign coffers, hinting that some of the money might come from "foreign sources."

"It bothers me, all these unattributed contributions," he told Democratic campaign workers outside Scranton. "Where is all this money from?"

The groups, including a pair launched by former Bush administration political operatives Karl Rove and Ed Gillespie, are spending tens of millions of dollars to help GOP candidates this year. They operate under recently liberalized rules that allow them to raise unlimited amounts of money from individuals and corporations.

"Karl Rove has gone out, because there's no longer a requirement to disclose who contributes to you, and gathered up tens of millions of dollars. We don't know if they're coming from foreign sources. We have a pretty good idea where a lot of it's coming from: very conservative millionaires," said Biden, who appeared Monday at fundraisers for a trio of endangered House Democrats.

He continued: "I challenge Karl Rove to tell me that this money isn't coming from billionaires and millionaires, insurance companies, oil companies, major executives" who have little in common with most voters.

Biden's remarks echoed allegations made in a new Democratic National Committee advertisement that accused Rove and the U.S. Chamber of Commerce of "stealing our democracy, spending millions from secret donors to elect Republicans to do their bidding in Congress."

Rove, appearing on "Fox News Sunday," said Democrats "have not one shred of evidence to back up that baseless lie. ... Have these people no shame?"

Republican National Committee spokesman Parish Braden said Monday in response to Biden that the vice president was trying to distract voters from high unemployment and continued job losses caused by "the Obama administration's destructive economic agenda."

Biden, pleading Monday for another two years of Democratic control, said Republican plans to deregulate Wall Street and corporations and to cut taxes for the wealthy are "exactly what got us where we are."

He characterized the House Republicans' "Pledge to America" as a "threat to America."

"If we do not maintain the House, and we do not maintain the Senate, we're in serious jeopardy of seeing everything turned around. We're just now beginning to climb out," Biden said.

Amid stops for Democratic Reps. Chris Carney, Kathy Dahlkemper and Mark Critz, the vice president squeezed in a tour of his childhood home in Scranton and greeted old friends who had assembled at Carney's campaign office in Dickson City.

Later Monday in Pittsburgh, Biden stopped at an ice cream parlor and greeted customers while eating whitehouse cherry ice cream in a waffle cone. A couple at one table, both Democrats, told Biden they were concerned about the GOP winning seats in November.

"Well, we're going to be just fine," Biden said.

Biden predicted that Democrats will hold on to the House and Senate once voters consider the alternative -- Republican policies that he said plunged the nation into recession.

He said he understands people are angry about the economy, but that Republicans would make things worse.

"When people are angry, they want to focus on their anger. If this is a referendum on anger, we lose. If this is a referendum on choice, we're going to win," said Biden.

Republicans tried to turn Biden into a campaign liability for Democratic incumbents.

"The vice president's weekly appearances in the state just remind voters that partisan Democrats like Chris Carney, Kathy Dahlkemper and Mark Critz continue to champion an agenda of higher taxes and reckless spending that has undercut Pennsylvania's path to recovery," Braden said.