"Can you quantify the likelihood that [Ryan] will be able in 2080 to deliver on a voucher that's a quarter the size that it is today in purchasing power, as opposed to the likelihood of [the reform law] going forward as written?" Rep. Earl Blumenauer (D-Ore.) asked Medicare chief actuary Rick Foster, the sole witness.
Foster said that "potentially" the vouchers would also be under great price pressure.
Democrats weren't able to prevent all attacks on their bill, however.
Asked if the law fulfills its promise to lower healthcare costs for Americans, Foster answered: "I would say false."
Foster and his team have estimated that the law would increase national healthcare costs by $311 billion through 2019.
The Republican leadership has not adopted Ryan's Medicare proposal as its own. They did, however, choose their rising star to give the Republican response to the president's State of the Union address Tuesday evening.
Early in the hearing, Ryan said it was interesting that Democrats were spending a lot of time attacking his roadmap rather than defending their bill. But Rep. Chris Van Hollen (D-Md.), the top Democrat on the panel, said Ryan opened the door open to criticism when he mentioned an "alternative" to the Democrats' law in his opening statement.