As much as Newt Gingrich’s supporters wanted to believe his rise in the polls was more solid than Rick Perry’s or Herman Cain’s, it looks like his reign on top is coming to an end. Jonathan writes that Gingrich has plummeted to 14 percent in today’s Public Policy Polling Iowa survey, down from 22 percent last week and 27 the week before.

While we may just be witnessing the beginning of Gingrich’s collapse, his trajectory has seemed to follow the same pattern as the previous not-Romney frontrunners, who maintained their leads for a little more than a month before crashing spectacularly. But there are reasons why Gingrich’s fall may not be as dramatic as the other ones, according to the National Journal:

Gingrich’s candidacy does have several variables that could complicate whether he too falls just as hard. For one, it’s not readily apparent which candidate conservative voters could flock to instead. In every other case, when a GOP candidate flopped there was a concurrent rise in one of their rivals. Bachmann was succeeded by Perry, who was supplanted by Cain, who gave way to Gingrich.

So far, no candidate seems to be rising to fill in the “not-Romney” void that would be left by Gingrich. Rick Santorum and Ron Paul have gained a modest two points since last week’s PPP poll, while Michele Bachmann, Rick Perry and Jon Huntsman have basically remained flat.

Paul is now leading the field at 23 percent, with Romney on his heels at 20 percent. According to PPP, Romney has the most to gain from Gingrich’s fall:

One thing Romney really has going for him is more room for growth than Paul.  Among voters who say they’re not firmly committed to their current candidate choice, Romney is the second choice for 19 percent compared to 17 percent for Perry, 15 percent for Bachmann, and only 13 percent for Paul.   It’s particularly worth noting that among Gingrich (who seems more likely to keep falling than turn it around) voters, he’s the second choice of 30 percent compared to only 11 percent for Paul.

Predictably, Paul’s supporters are the most committed to their candidate. But Paul’s ceiling in Iowa is also lower than Romney’s. If no other candidate rises to take Gingrich’s place, and this remains a two-man race between Paul and Romney until the caucuses, then there’s a good chance Romney could come out of Iowa as the victor.