Everyone’s a suspect.

In an apparent push poll, a research firm has called Iowa Republicans this week praising John McCain and critcizing Mitt Romney and his Mormon faith…

[T]here were “lots of negatives on Romney,” said the recepient of the call in an e-mail, including mentions of his “flip-flops,” hiring illegal immigrants as landscapers and extensive discussion of Mormonism.

“Statements were on baptizing the dead, the Book of Mormon being on the level of the Bible, and one about equating it to a cult,” said the Iowan, deeming them “common criticisms of Mormonism.”

“I think they asked twice if being a Mormon would be an issue,” this person added.

McCain’s camp “emphatically” denies responsibility. Not only that, but:

Another McCain source … said tonight that the calls had been traced back to a number linked to the Tarrance Group — Rudy Giuliani’s pollster.

Giuliani’s spokewoman and a pollster at Tarrance categorically deny that he’s responsible. Romney’s communications director calls the unknown guilty party “repulsive” and “un-American.” Politico links to an AP story, meanwhile, noting similar calls in New Hampshire and connecting them to a firm that worked with Tarrance in 2006.

Exit question: Whodunnit?

Update: McCain’s famously strapped for cash. Would he really be dumping money into stuff like this when he could be putting it to better uses?

Update: An update at Politico quotes the Tarrance pollster as wondering if the poll might have been commissioned by a 527 organization. If so, did they do so at a candidate’s behest, to provide plausible deniability?