Mitt Romney’s bad week – which looks like it may get much worse before it’s over – just took another hit from a gloomy Gallup poll. Unlike other recent surveys, which have shown Romney dropping below Newt Gingrich in South Carolina, this one was a poll of national voters (via HotAir):

Gallup’s Editor-in-chief Frank Newport appeared on MSNBC to talk about the polling organization’s national tracking poll of the GOP primary race, which is changing rapidly in the last few days of the campaign for South Carolina. Newport said when their new data comes out at 1 pm eastern, “…we’ll see this gap closing more. Romney was up 23 points over Newt Gingrich. Now it will be down about ten points, so clearly things are collapsing.” …

“We have seen more movement, more roller coaster kind of effect this year than any other Republican primary in our history of tracking,” Newport said. “I think anything is possible. It wouldn’t be out of the realm of possibility if Romney recovers. We’ll wait and see.”

Ed Morrissey notes two reasons for reading this poll with caution: it was a survey of registered voters, not likely voters, and it was also taken before the interview with Gingrich’s wife aired.

But the “bombshell” allegation about Gingrich wanting an open marriage had already received heavy media attention well before the interview even aired yesterday, and the actual Nightline report didn’t add much more to the story. Gingrich was also able to deflect the controversy pretty effectively with his scathing response to John King last night. So while it may still have an impact, it’s also very likely that it won’t be enough to move the dial.

It’s amazing how a single day has completely changed the dynamic of this race. Less than a week ago, Romney was expected to coast to the nomination. Now he lost Iowa, appears to be headed for defeat in South Carolina, and is slumping nationally — all in a span of 24-hours.