In a whispering campaign not ready to go public, some senior Republicans are so anxious about the state of the GOP race they are actually considering the unheard of: a scenario that would lead to another candidate entering the Republican primary race, and potentially an open convention.

They are not unhappy enough, however, to go on the record calling for another candidate to enter the fray. In fact, when pressed, many Republicans say the chatter about another candidate is inevitable in this long and inconclusive primary process. They also say it's just not likely to happen.

Why?

"If you bring somebody new into the race, that person will lose," said a senior GOP strategist who admits a bias towards Romney. "The party -- especially conservatives -- will not respond to somebody who has not gone through the process.'

That being said, it's clear Rick Santorum's recent rise in the polls -- and what some see as his electability problems -- have struck a nerve with Republicans.

"There is something called agenda control," said one unaffiliated GOP strategist. "Santorum does not have it. Instead of talking about the economy, he's been going down rabbit holes for the last four or five days."

Santorum's emphasis on cultural issues may intensify his conservative and evangelical support and help him win the nomination or at least differentiate himself from Newt Gingrich. The fear is he may also be narrowing his support in a general election population.

And Santorum's surging candidacy is not the only concern for senior Republicans. Mitt Romney's inability to close the deal has also raised eyebrows -- and angst. And the anxiety will only intensify should Romney lose his home state of Michigan in the primary on Feb. 28, several senior Republicans told CNN.

"Michigan is the whole shooting match," said one senior GOP strategist not aligned with a campaign. Said another: "If Romney loses Michigan, all hell breaks loose."

Given that real possibility, one knowledgeable GOP source confirms that some Republicans are circulating the deadlines and the basic math that would allow another candidate to get into the nomination fight and take it all the way to the convention. More than a half dozen states' filing deadlines have yet to pass. A majority of the delegates to the national convention are still up for grabs. One more factor to be considered: many states are choosing their delegates proportionally, which makes it easier for a candidate pick up delegates without outright winning a state.

Politico first reported the existence of a document circulating among Republicans.

Santorum's highlighting of cultural issues could play well for him in the short-term. But the worry among Republicans is that his views will raise the question of his electability. "After a while, Republican voters will start asking whether this is the guy to take on Obama," says one GOP strategist. In addition to the fear of a potential loss to Obama, some Republicans worry about losing the House of Representatives if Santorum were at the top of the ticket.

"Santorum would so alienate voters, especially women...he would be lucky to carry a dozen states," one senior Republican told CNN, referring to Santorum's disapproval of pre-natal screening.

Santorum's campaign disagrees. It considers him a strong social conservative who is the best equipped to take on President Obama on the economic issues -- -particularly in the rustbelt states. "He won in Pennsylvania, which has both democrats and women the last time I checked," says a senior Santorum adviser, who calls his boss a "full spectrum conservative."

One of the Republicans who has seen the memo said "no one is hoping that this will come to play," regarding a new candidate entering the fray. Yet some Republican partisans feel they need to make some contingency plans depending on the outcome in coming primaries. Other veteran Republicans contacted by CNN dismissed any possibility of another candidate entering the contest at this date.

There are no names of possible candidates mentioned in the memo. Who would the Republicans possibly turn to? The usual suspects include Sarah Palin, Indiana Gov. Mitch Daniels, New Jersey Gov. Chris Christie or Former Florida Gov. Jeb Bush. They could still enter the race although they all have repeatedly said they will not mount a campaign despite new inquiries by some in the party.

"I really would not be interested," Daniels told CNN affiliate WISH Monday. "If we get to that point, I would be interested in finding someone who can present a really credible and winning alternative to where the nation is going right now. I still think it's very unlikely. These things have a way of resolving themselves."