A month ago, Newt Gingrich floated the idea of an alliance with Rick Santorum to defeat Mitt Romney for the nomination.  He didn’t exactly specify who would be the leader of that alliance when he floated the notion to Laura Ingraham, but Santorum certainly didn’t get lulled into the idea that he would shortly get an endorsement from Gingrich — nor did he demand one, along with an exit from the race.  Gingrich has demanded the latter, at the very least, from Santorum — and as Robert Costa reports, it’s getting mighty testy in the “alliance” these days:

Tensions between the Santorum and Gingrich camps are growing. Santorum advisers are irked at Gingrich’s public attempts to nudge their candidate out of the race; Gingrich aides are frustrated by Santorum’s quixotic determination, his unwillingness to cede the anti-establishment mantle.

Earlier this week, in a Fox News interview, Gingrich verbalized his inner circle’s agitation. “The longer conservatives stay split, the harder it’s going to be for us to [beat Romney],” he said. “We risk not being able to beat Obama unless we get a conservative. I have to win the nomination.”

Santorum confidants chuckle at Gingrich’s declaration. “Gingrich’s stock is falling, and we’re picking up a lot of his people,” says John Brabender, Santorum’s senior strategist. “People know that we need an alternative to Mitt Romney. But Gingrich had his shot in Florida, and he failed.”

And  it’s getting personal.  Gingrich made that demand at the same time that Santorum and his family were still dealing with his daughter Bella’s health crisis.  That has infuriated Santorum’s staff, especially since only one of Santorum’s competitors failed to call and offer his best wishes during that crisis:

The timing of Gingrich’s comments — they came around the time Santorum was tending to Bella, his hospitalized daughter — inflamed the fractious relations between the two campaigns. “The mere fact that he was doing it smells of political opportunism and people found it problematic and troubling,” Brabender says.

“Beyond that, I won’t talk about Gingrich,” Brabender says. “I will compliment Governor Romney and Congressman Paul. Their campaigns personally reached out to us [regarding Bella]. None of that was expected, so I won’t criticize anybody for not doing it. But that was very sincere and gratifying.”

Costa’s sources on Team Gingrich apparently admitted that Gingrich made a mistake on timing that demand, and now say that they don’t expect Gingrich to make further demands … at least not publicly.  Surrogates for Gingrich will start reaching to Santorum’s surrogates to put some pressure on the Senator to get out of Gingrich’s way and turn this into a two-man race.  So far, though, Santorum’s team says that no one’s telling them to get out — at all:

Nevertheless, Santorum sources say the raw wound between the pair is unlikely to heal, even if Gingrich backs off. “We’re not getting calls from big conservatives,” says one Santorum source. “That’s not happening at all. Many Republicans don’t want Mitt to be the nominee. They also know that Gingrich can’t beat Mitt. They’re waiting to see if we can make a move in February.”

Besides, there is a very real question as to whether Gingrich would get Santorum’s voters anyway.  One way to measure potential upside is through favorability ratings, and those show that Gingrich has a lot less upside than Santorum.  Gingrich’s favorability in states like Nevada and Arizona are very low, even among Republicans.  As noted earlier, Santorum beats Gingrich as a second choice in Nevada 30/16, with Romney at 13, which makes more of an argument for Gingrich’s withdrawal.  In Missouri and Ohio, two key Republican states, PPP shows Santorum beating Romney head to head, not Gingrich:

-In Missouri Santorum leads Romney 50-37 and in Ohio Santorum leads 45-38.

-In Missouri Gingrich leads Romney 43-42 and in Ohio Gingrich leads 42-39.

Two takeaways from those numbers: if this ever came down to Romney, Paul, and just one out of Gingrich and Santorum, Romney would be in a lot of trouble. And he’d be in more trouble if the single conservative alternative ended up being Santorum.

Based on the limited polling for second choices (only PPP regularly asks the question), it’s not definitive which candidate would benefit more from the absence of the other, but it’s even less clear that the absence of Santorum would block Romney from winning the nomination.