With recent polls showing Republican presidential hopeful Mitt Romney either trailing or at best tied with Rick Santorum in the Michigan primary, some Republican leaders are starting to get nervous.

One "prominent Republican senator" told ABC News senior political correspondent Jonathan Karl on Friday that “if Romney cannot win Michigan, we need a new candidate,” because with such a weak nominee "we'd get killed" in the general election.

He insisted that he expects Romney to eventually prevail in Michigan, but stated that “if he can’t even win in Michigan, where his family is from, where he grew up ... he'd be too damaged" to run a successful presidential campaign.

The unidentified source also expressed the opinion that neither Rick Santorum nor Newt Gingrich would be an acceptable choice, because they would "lose 35 states," and named former Florida Governor Jeb Bush as his preferred alternative.

Meanwhile, Romney continues to come under fire from a variety of directions, with Salon's Glenn Greenwald now accusing the national finance co-chair of Romney's campaign -- who is also a million-dollar donor to the pro-Romney Restore Our Future Super-PAC -- of using threats to silence his critics.

According to Greenwald, Idaho billionaire Frank VanderSloot has previously run into legal problems involving charges that his dietary supplement company was running a pyramid scheme and that it was deceiving customers about its products.

"But it is VanderSloot’s chronic bullying threats to bring patently frivolous lawsuits against his political critics — magazines, journalists, and bloggers — that makes him particularly pernicious and worthy of more attention," Greenwald writes. "In the last month alone, VanderSloot, using threats of expensive defamation actions, has successfully forced Forbes, Mother Jones and at least one local gay blogger in Idaho to remove articles that critically focused on his political and business practices. .... He has been using this abusive tactic in Idaho for years: suppressing legitimate political speech by threatening or even commencing lawsuits against even the most obscure critics."

"Numerous journalists and bloggers in Idaho — who want to write critically about VanderSloot’s vast funding of right-wing political causes — are petrified even to mention his name for fear of these threats," Greenwald continues. "As his work on the Romney campaign brings him national notoriety, he is now aiming these tactics beyond Idaho."

Greenwald goes on to document his charges against VanderSloot in detail, focusing on the case of Idaho independent journalist and LGBT spokesperson Jody May-Chang, who "is determined not to succumb to this bullying or to relinquish her right to opine and report on the conduct of a very significant political figure in her state."

"Anyone who is the national finance co-chair of Mitt Romney’s presidential campaign deserves probing, substantial scrutiny," Greenwald concludes. "That’s equally true of someone who continues to use their vast wealth to influence the outcome of our elections and our most inflammatory political debates. And it’s certainly true of someone who has made it a regular practice of threatening journalists, bloggers and activists who shine light on his political and business practices."

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