Meanwhile, Republicans, including Gerlach, are reviving their 2010 arguments that helped shift seniors' trust on Medicare from Democrats to Republicans. This is the second time that Trivedi has challenged Gerlach, and Gerlach is reprising the arguments that won him 57 percent of the vote in 2010.

"The Democrats complaining about serious efforts by Republicans to actually save Medicare are both a joke and a disgrace," Gerlach said. "They self-righteously posture like they care about seniors, but they have never put forth a proposal that will save the program."

The argument is an even easier sell this time around, Gerlach said in an interview, because the Congressional Budget Office recently revised its original estimate about how much the health law would reduce the growth of Medicare spending.

"They're cutting $716 billion out of Medicare today for existing seniors," he said. "Our proposal wouldn’t affect existing seniors. Voters get that, and that’s why it’s an easier issue to talk about than it was two years ago."

The Ryan proposal assumes the same $716 billion in reductions.

Trivedi supporters at the Exeter event acknowledged they understood very little about Ryan's Medicare proposals — and some of what they said they knew was inaccurate. Regardless, most said that Medicare was extremely important to them and that it was a top voting issue. Before the end of the evening, many had signed up to make phone calls, stuff envelopes, and do what they could to help defeat Gerlach — and Ryan’s Medicare plan.

"I see [Medicare] as a big issue because next year I'm eligible," said Nancy Daubert of Spring Township in Berks County. "The idea that Ryan would take the safety net away from so many people is appalling. … They say it will cost me $6,300 more. I don’t know where that comes from, but it's a big concern for me."

Bellwethers or flukes?

Anna Greenberg, a Democratic pollster and senior vice president of Greenberg Quinlan Rosner Research, said the Democratic strategy has already proven successful in special elections in Arizona and New York, where the Democratic candidate claimed that Republicans were trying to privatize Medicare and increase seniors' costs.

"The Ryan plan is an albatross, and every Republican voted for two Ryan budgets," she said.

While Greenberg calls those contests bellwethers, Wasserman says they were races in which Republicans held extreme positions on the issue. Republicans beat back a similar effort in a special election in Nevada last year, in part by mounting a strong offense against the health care law — a strategy that Republicans are trying to duplicate in this year's races.

But Kathy Boockvar, a Pennsylvania Democrat challenging Republican freshman Michael Fitzpatrick, continues to believe the issue will be decisive.

"This is a very significant part of my campaign," she said in an interview. "I think we'll pull back some seniors to the left."

Also of interest: Power of the 50-plus voter.