Conservatives will be thrilled with the selection of their favored pick, Rep. Paul Ryan (R-Wis.), as Mitt Romney’s running mate, but Democratic campaign operatives may be just as excited.

In recent years, Democrats have used that provision to argue that Republicans will “end Medicare as we know it” or just plain “end Medicare” — although the latter claim has been criticized as stretching the truth.

Either way, the line of attack has proved potent. Democrats and Republicans acknowledge that it helped Democrats win recent special elections in conservative districts in upstate New York and Arizona.

Democrats need to win 25 House seats to retake the chamber. They need to lose no more than three Senate seats to keep their majority there. The Senate is considered to be in play in 2012, with Democrats defending many conservative-leaning and swing states.

Democrats say putting Ryan on the ticket will push his budget to the forefront even more and force Republicans who haven’t already taken a position on it to do so. And they moved quickly Saturday to rehash the issue with just three months to go before the 2012 election.

“His plan . . . would end Medicare as we know it by turning it into a voucher system, shifting thousands of dollars in health-care costs to seniors,” President Obama said in a statement on Ryan’s selection.

“Congressman Paul Ryan and Mitt Romney are a match made in millionaires’ heaven, but they’ll be a nightmare for seniors who’ve earned their Medicare benefits,” said Rep. Steve Israel (D-N.Y.), chairman of House Democrats’ campaign committee.

Poll after poll shows that Americans, while wanting to cut waste in the budget, are strongly resistant to any major cuts or changes in federal entitlement programs. By proposing to overhaul Medicare, Democrats argue, Ryan has handed them an ace in the 2012 election, in large part because many members of the House have voted for the budget and can easily be attached to it.

Republicans, many of whom have acknowledged that the Ryan budget puts them in an uncomfortable spot politically, argue that his selection changes little, because they were already going to be attacked on the issue regardless in 2012.

In addition, they say they have neutralized the issue by effectively pointing to $500 billion in Medicare cuts contained in Obama’s budget — a strategy that helped them win another recent special election in a competitive district in Nevada.

Democrats tried to attach now-Rep. Mark Amodei (R-Nev.) to Ryan’s budget in that race, but the attack was blunted in part because Republicans were able to accuse Democrats of also wanting to cut Medicare.

A recent poll from Democratic pollster Democracy Corps showed that, when the Ryan budget is described the way Republicans would like in battleground House districts, 52 percent of voters say they support it, while 37 percent oppose. When the budget is described as attempting to “save Medicare,” Republicans do well.

In addition, Republicans note that the poll shows they are still winning the senior vote in these districts.

Democrats “concede that victory or defeat will be determined by their ability to make the Ryan budget so incredibly toxic that seniors alone will oust the Republican majority,” the National Republican Congressional Committee said in a recent analysis. “Now, 90 days from the election, according to polling data from the Democratic firm Democracy Corps, there are clear signs of failure for House Democrats on the issue.”

When it is noted, however, that the Ryan budget “slashes and privatizes Medicare,” the poll shows 66 percent of voters say they have “serious doubts” about it.

“Medicare is a key reason why voters reject the Ryan plan — but while Medicare is a potent and predictive element in the Ryan budget, it is hardly the only concern voters have about the Republican plan,” said Democratic pollster Stan Greenberg and strategist James Carville.

The GOP is currently honing its message to emphasize protecting the entitlement and attacking Obama’s cuts.

“Unlike the current president, who has cut Medicare funding by $700 billion, we will preserve and protect Medicare and Social Security,” Romney said in announcing Ryan as his pick Saturday in Norfolk, Va.

As a recent New York Times piece points out, the cut Obama was proposing is also contained in the Ryan budget. But Republicans note that with both sides being accused of cuts, they can muddle the issue.

Analysts generally agree that the Ryan budget poses problems for the GOP. Republicans have had to vote for it and press the issue, they argue, because the conservative base expects them to do something with their newfound House majority.

“For many seniors, doing anything to Medicare that can’t be portrayed as an increase is essentially a cut, and they will fight it to their last breath,” political analyst Charlie Cook wrote last year. “From a political standpoint, Medicare reform is very dangerous territory. House Republicans are not just pushing the envelope — they are soaking it with lighter fluid and waving a match at it.”

House Republicans have now voted twice in favor of the budget, while Senate Republicans have also voted for it. In each case, few Republicans voted against their party.

And one of the few House Republicans to vote against — Rep. Denny Rehberg (R-Mont.) — has benefitted from ads funded by state and national Republicans touting his opposition to the bill in ads for his Senate campaign.

In a statement Saturday, Rehberg alluded to his vote against the GOP budget but praised Ryan’s selection.

“Congressman Ryan is a public servant of the highest order, and I appreciate his character, intelligence, and creativity, not only on the vast majority of issues on which we agree — like controlling government spending, developing our natural resources, and providing tax relief for families and job creators — but also on the few occasions where we haven’t,” Rehberg said.