Presidential campaigns hardly ever release internal polling, so from the outside, we don’t know if the candidates are getting encouraging or discouraging news from their pollsters.

But when it comes to Mitt Romney’s campaign, there’s no real need to guess. When these guys are feeling confident about the Republican primaries, they’re going after President Obama. When they’re feeling nervous, they’re attacking Republicans. Which ones? Whichever ones the internal polls point to as a potential threat.

And right now, we know exactly who’s making Romney and his team nervous.

With three days to go before the South Carolina primary, the Mitt Romney campaign is taking on Newt Gingrich with a ferocity not seen in weeks.

On Wednesday, former Sen. Jim Talent (R-MO) and former Rep. Susan Molinari (R-NY) — both of whom served under Gingrich as House Speaker — excoriated their old leader on a conference call hosted by the Romney campaign.

Their appearance on the call is part of a new rollout of negativity against Gingrich by the Romney campaign featuring web videos by the pair at the Romney website

The attacks are interesting in their own right, with Romney’s surrogates arguing that Gingrich isn’t reliable on conservative issues. We can only assume that Romney’s surrogates have no knowledge of their own candidate’s background, beliefs, or never-ending series of flip-flops.

But the larger point is that this call wouldn’t have even been organized if Romney assumed a South Carolina victory was in the bag. Most polls show him with a comfortable lead, but with a few days to go, the former governor’s campaign seems to believe it has cause for concern.

What’s more, it’s not just Gingrich. The Romney campaign has a new robocall in the field — Team Romney is outspending the other candidates on automated calls, 5 to 1 — targeting Rick Santorum. This one is intended to exploit Santorum’s 2008 support for Romney, when the former senator hoped to derail John McCain’s nomination:

AUDIO TEXT: “This is an urgent message from the Romney campaign. In 2008, Rick Santorum made the following announcement on Laura Ingraham’s radio program.”

LAURA INGRAHAM: “Joining us now with an important announcement, you’re not going to want to miss this, former senator from the great state of Pennsylvania, Rick Santorum.”

RICK SANTORUM: “If you’re a conservative, there really is only one place to go right now. I would even argue farther than that. If you’re a Republican, if you’re a Republican in the broadest sense, there is only one place to go right now, and that’s Mitt Romney.”

LAURA INGRAHAM: “Senator Rick Santorum endorsing Mitt Romney unequivocally, without hesitation, that should mean something to all of you. Senator Santorum, thank you so much.”

The call appears to give voters the impression that Santorum supports Romney now, as opposed to four years ago.

Again, if Romney wasn’t worried, none of this would be necessary.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.