U.S. House of Representatives

Democratic Rep. Chris Van Hollen of Maryland has been tapped to play his congressional arch rival, Rep. Paul Ryan, in upcoming rehearsals to prepare Vice President Joe Biden for his single televised election-year debate, Obama campaign officials confirmed to ABC News.

Van Hollen, the ranking member on the House Budget Committee, which Ryan chairs, is the party's leading voice on budget policy in the Congress. He has studied Ryan's signature plan and arguably knows it better than most on Capitol Hill.

An articulate and aggressive debater, he is also a regular on the TV cable news circuit and on the Sunday morning talk shows.

"I've said that Mitt Romney's choice of Paul Ryan to the ticket has definitely sharpened the debate and made even more clear the choice for the American people," Van Hollen told reporters today on a conference call to discuss competing plans for Medicare.

"At its core, the Ryan-Romney budget provides huge tax cuts to the very wealthy, like Mitt Romney, at the expense of everyone and everything else," he said, before launching into a 10-minute prosecution of the plan that demonstrated his handle on the issues and eagerness to debate.

Democrats believe Van Hollen will be an able stand-in for the Republican vice presidential nominee Ryan. It's unclear, however, when Biden, 69, will begin debate preparations in earnest. He and Ryan, 42, will face-off in Danville, Ky., on Oct. 11.

Meanwhile, President Obama will be preparing for his two televised debates with Mitt Romney by sparring behind closed doors with former presidential nominee Sen. John Kerry of Massachusetts. Obama and Romney will debate three times in October.

Van Hollen will appear Sunday on a special edition of ABC's "This Week" for a roundtable debate on U.S. fiscal policy coordinated in partnership with the University of Virginia's Miller Center.

Get more pure politics at ABC News.com/Politics and a lighter take on the news at OTUSNews.com