Presumptive GOP presidential nominee Mitt Romney’s attempt to bolster his new running mate’s deal-making credentials drew a sharp rebuke from the Democratic Senator at the center of the supposed bipartisanship.

At a Saturday campaign stop with his new vice presidential pick, Rep. Paul Ryan (Wis.), Romney praised the House Budget chairman’s work with Democratic Sen. Ron Wyden (Ore.) to develop a Medicare overhaul plan.

“This man said, ‘I’m going to find Democrats to work with.’ He found a Democrat to co-lead a piece of legislation that makes sure we can save Medicare,” Romney said in Ashland, Va. “Republicans and Democrats coming together. He’s a man who has great ideas and the capacity to lead to find people to cross the aisle – to work together.”

Wyden was quick to push back on Romney’s version of events.

“Gov. Romney is talking nonsense. Bipartisanship requires that you not make up the facts. I did not ‘co-lead a piece of legislation.'” Wyden said. “I wrote a policy paper on options for Medicare. Several months after the paper came out, I spoke and voted against the Medicare provisions in the Ryan budget.”

Ryan and Wyden did work together in December 2011 to develop a paper outlining ways to provide for Medicare solvency, including a “premium support” model. Under premium support, Medicare would allow a menu of competing plans to offer coverage with government payments. Wyden, however, never signed on to support the House-adopted budget resolution written by Ryan that included plans for a premium support approach.

“Gov. Romney needs to learn you don’t protect seniors by makings things up, and his comments today sure won’t help promote real bipartisanship,” Wyden said.

Wyden has voted against House Republican budgets when they have received votes in the Senate. Republican aides were quick to circulate the Wyden-Ryan Medicare report after the announcement that Ryan would be joining Romney on the GOP presidential ticket.

Democrats are already reprising one of their familiar lines, saying Ryan’s budget plan would “end Medicare as we know it.” That exact phrase appeared in separate statements issued Saturday by Obama campaign manager Jim Messina, Senate Majority Leader Harry Reid (Nev.) and House Minority Whip Steny Hoyer (Md.).

The mere fact that Wyden was at one point involved in Ryan’s Medicare proposals could undermine that Democratic message – and Wyden seems to know it.