Could Democrats’ perceived strength on the issue of Medicare reform wind up being a major weakness?

View Photo Gallery: Five things you didn’t know about Paul Ryan.

In the days leading up to Mitt Romney’s running-mate announcement, the conventional wisdom among members of both parties on Capitol Hill has been that House Budget Committee Chairman Paul Ryan (R-Wis.) would be among the boldest picks the presumptive GOP nominee could make — but that the move would be a non-starter since it would open up the GOP ticket to a barrage of Democratic attacks on Ryan’s much-debated budget blueprint.

That C.W. seems to have gone out the window with the news that Romney is expected to tap Ryan for the No. 2 spot this morning at a campaign event in Norfolk.

While Democrats have had success this cycle in hammering Republican congressional candidates over the Ryan budget — particularly its proposed overhaul of federal entitlement programs such as Medicare — there’s a case to be made that when it comes to the budget debate, Democrats could face as much risk as they do reward.

The reason? If Democrats slam the GOP ticket with the familiar charge that the Ryan plan would “end Medicare as we know it,” Republicans have a counter-argument at the ready: namely, that Democrats backed a national health care law that trims $500 billion in federal spending on the health-care program for the elderly and disabled.

It’s an argument that boosted Republicans in the 2010 midterms and one that more recently has been used successfully by candidates such as Mark Amodei, the Republican who bested Democrat Kate Marshall in last September’s special election in Nevada’s 2nd Congressional District. The district went narrowly for Sen. John McCain (R-Ariz.) in 2008.

Amodei’s campaign countered Democrats’ Medicare-themed attacks in part by running ads featuring the candidate’s mother defending him and charging that Marshall was the one who supported cuts to the popular entitlement program.

On the day of the special election, Amodei not only bested Marshall by a 22-percentage-point margin, but GOP polling showed that Amodei had come to be viewed by voters as the more trusted candidate on the Medicare issue.

“The Democrats attacked hard with ‘Mediscare’ ads, but we defended and counterpunched hard with Obamacare’s $500 billion cut,” said Rob Stutzman, a California-based GOP media strategist who worked as ad consultant for Amodei’s campaign. “We wanted to fight Medicare to a draw but actually won the issue by Election Day.”

“Democrats have vulnerabilities on the issue,” he added.

Of course, for every point there’s a counterpoint, and national Democrats cite the more recent example of this June’s special election in Arizona’s 8th District, where former Gabrielle Giffords aide Ron Barber (D) bested Republican Jesse Kelly in a hotly contested race in which Medicare loomed large.

One ad run against Kelly by the Democratic Congressional Campaign Committee featured a middle-aged construction worker named Noel Hatfield who stated that he had paid into Medicare ever since he started working at age 15.

“Jesse Kelly’s said that over time, he’s going to get rid of Medicare,” Hatfield said in the ad. “I don’t think it’s right for Jesse Kelly and people to decide that I don’t get my Medicare that I’ve been paying for.”

Democrats have argued that such ads helped propel Barber to his 6 percentage point victory over Kelly in a GOP-leaning district and that similar TV spots would be effective against Republicans across the country, including at the presidential level.

On top of that, Democrats appear poised to strike back quickly at Republicans over the $500 billion claim. No sooner had we tweeted early Saturday morning about the possibility of a presidential-level fight over the issue than a Democratic operative passed on a memo pointing out that the Ryan budget would maintain the same cuts for which Republicans have slammed their Democratic counterparts on the trail.

“We talk about the Ryan budget kind of a lot,” the operative quipped.

So which side is better off on the issue?

The answer will likely come into clearer focus as the dust settles on Romney’s V.P. pick. But in the meantime, it’s worth considering that last year’s special election in New York’s 26th District — another race that hinged on the Ryan budget and Medicare, and one that was won by Democrats — was deemed by to be “a national test market for distorted political claims.”

The New York Times’ Jackie Calmes in July noted the “messaging mess” that has become of the Medicare debate.

And The Washington Post’s Fact Checker, Glenn Kessler, has called out both parties for mischaracterizing the other side’s stance on the issue.

In short, if you thought that Mitt Romney’s choice of Paul Ryan would usher in a new phase of the presidential campaign focused squarely on issues and ideas, think again.

And if you thought the candidates’ messaging battle was an already bewildering one, the past few months have been only the beginning.