Republican candidates are being pushed to take a position on the budget proposed b Rep. Paul Ryan (R-Wis.). (Charles Dharapak/AP)

But that counsel is also rapidly becoming unrealistic as the Ryan plan, passed by the House in April, is evolving into the litmus test for Republican candidates fighting key 2012 Senate primaries in places like Florida, Missouri and New Mexico. The outcome of those races could help determine the shape of Congress in 2013.

On the campaign trail, conservatives are already pushing Republicans to embrace Ryan’s plan in the primaries, and so are Democrats, who hope to use the Medicare overhaul against the GOP in the general election.

The plan’s most controversial element is a proposal by Ryan to convert Medicare into a voucher-like program by 2022. After the House passed the Ryan plan in April, 235 to 123, Republicans were targeted by both sides for their support of it.

Democrats used the vote to their advantage in the New York special election that resulted in a victory by Rep. Kathy Hochul (D), while former House speaker and 2012 presidential candidate Newt Gingrich earned his colleagues’ — and conservatives’ — vitriol for calling the plan “right-wing social engineering.”

Most other races are a year-and-a -half away, and Democrats will have to work harder to keep the Medicare issue at the forefront of voters’ minds. And, Republicans argue that Democrats are equally liable as they voted for Obama’s 2010 health-care law, which also cut Medicare.

“That vote is real and one that every Senate Democrat will have to defend next year,” predicted National Republican Senatorial Committee communications director Brian Walsh.

Of course, the health-care vote was signed eight months before the 2010 elections. It still had a significant (and negative) impact for Democrats.

In the short-term, the Medicare issue is already causing headaches for Republicans in key primaries around the country.

In the GOP primary to take on Sen. Bill Nelson (D-Fla.), state Senate President Mike Haridopolos was forced to take a position on the Ryan plan after a painful interivew with a conservative talk-radio host in which he tried to evade the issue. Haridopolos eventually said he would have voted against the Ryan budget, because of the Medicare cuts. His primary opponent, former state Rep. Adam Hasner, accused him of standing with Democrats. The issue is likely to be a key one in Florida, which has a large population of senior citizens dependent on the program.

In New Mexico, neither candidate in the primary for the open Senate seat being vacated by retiring Sen. Jeff Bingaman (D) has yet committed to voting for Ryan’s plan. Yet it’s still become an issue in the contest.

Former Rep. Heather Wilson (R) is being attacked by primary opponent John Sanchez for praising Ryan while voting against what he called a similar plan in 2007, when Wilson was in the House.

In the Ohio Senate race, former Secretary of State Ken Blackwell wrote an op-ed for National Review calling the Ryan budget “a line-in-the-sand moment for Republicans” — a possible shot at State Treasurer Josh Mandel, who has not taken a position. Mandel is challenging Sen. Sherrod Brown (D-Ohio); until today Blackwell was a likely primary challenger. In a statement to the Daily Caller, Blackwell said that he would not run, in part because “running would require me to make ‘nice’ with folks with whom I would rather not.”

Missouri’s Sarah Steelman, who is running in the GOP primary to challenge Sen. Claire McCaskill (D-Mo.), criticized the Medicare provisions in a high-profile video, only to say she she “would love to be able to vote for the Ryan plan” a few days later. That represented a shift in tone, if not an outright contradiction, that shows the difficulty of threading the needle on an issue that has divided the country. A representative of Steelman told Politico later, “She will stand up before the false vote and point out what’s wrong with it.”

Steelman’s primary opponent, Rep. Todd Akin (R-Mo.), voted for the Ryan plan — indeed, he helped craft it — so Medicare will likely be a big issue in their primary. Moreover, one of Steelman’s advisers, strategist Rick Wilson, called the issue “a litmus test with Republican voters.”

In the Virginia Senate race, former Sen. George Allen (R) has so far succeeded in not taking a stand on the Ryan plan. But he’s been criticized for not doing so by tea-party candidate Jaime Radtke and conservative businessman Tim Donner (neither is considered a terribly serious primary threat). It helps that Allen has released his own detailed policy proposals, although the Medicare portion of his plan is vague.

But Allen’s stance seems like a long-term strategy aimed at positioning himself in the general election, likely against former Virginia governor Tim Kaine (D), rather than in fending off a primary challenge.

In the House, Republicans won so many seats in 2010 that there are few competitive races where their candidates did not already vote for the Ryan budget. (After all, only four House Republicans opposed the bill.) In the handful of possible GOP pick-ups, it’s Democrats and reporters pressuring candidates to reveal their positions, not other Republicans.

Matt Doheny, a candidiate in New York’s 23rd ditrict against Rep. Bill Owens (D), has been asked by the local press to take a position. Rep. Tim Bishop (D), in New York’s 1st district, is pushing opponent Randy Altschuler (R) to take a stand.

With the Anthony Weiner scandal now behind them, Democrats are doing everything they can to re-focus on the Medicare question. If President Obama makes a deficit-reduction deal with Republicans that includes Medicare cuts, it will be harder for Democrats to keep up this line of attack.

Republicans also insist that the effect will ultimately be muted, because Senate Democrats voted for Medicare cuts as part of the health-care bill.

No matter which party supports them, entitlement cuts are not popular with voters as poll after poll has shown. Ryan’s Medicare plan in particular does not poll well.

That’s why some conservatives strategists have started to see the Ryan plan as a trap, urging their candidates not to embrace it. A Florida tea party leader called the proposal “a political trap and public policy nightmare, and the Republicans are locking arms jumping off the cliff for it!”

So far, however, that’s a minority view. For now, it looks like conservatives will join Democrats in pressuring Republican candidates to step up and speak out.