For months, there have been a couple of constants in the race for the Republican presidential nomination. The first is that Mitt Romney, no matter how obvious his success appeared, would be stuck in the low- to mid-20s. The second is that a non-Romney would break into the top tier, only to be replaced by another, then another, and then another.

It was a Romney-Pawlenty race. Then Pawlenty faded and it became a Romney-Bachmann race. When she faltered, we saw a Romney-Perry race. This was replaced with a Romney-Cain race.

And now it appears we have a Romney-Gingrich race. Here’s the new CNN national poll of Republican voters. (In the interests of space, I’m only including candidates with support in the double digits):

1. Mitt Romney: 24% (down two points since October)
2. Newt Gingrich: 22% (up 14 points)
3. Herman Cain: 14% (down nine points)
4. Rick Perry: 12% (down one point)

And here’s the new survey from Public Policy Polling, which was also released this afternoon (again, these are the only candidates to reach double digits):

1. Newt Gingrich: 28% (up 13 points since October)
2. Herman Cain: 25% (down five points)
3. Mitt Romney: 18% (down four points)

And in case anyone’s curious, separate polls from McClatchy and CBS News both show Gingrich’s support on par with Romney’s and/or Cain’s.

So, what can we take away from all of this? Well, for one thing, it’s probably fair to ask how much of Gingrich’s support is genuine, and how much of it is the result of Republican voters turning to him after trying and rejecting every other non-Romney candidate. Of course, either way, we appear to have a new Republican top tier.

For another, Cain’s sharp rise has now ended, undermined both by allegations of sexual harassment and his inability to deal with the charges coherently.

And finally, there’s the fact that Romney, despite being the clear favorite, just can’t figure out how to put some distance between himself and the rest of the Republican field. The Iowa caucuses are seven weeks from tomorrow, and the GOP frontrunner is seeing his support fall a little when he should be consolidating Republican support. Indeed, with Cain embarrassing himself, it stood to reason that some of his up-for-grabs supporters would settle for the former Massachusetts governor. Instead, they moved to the unlikable disgraced former House Speaker.

Romney is running against misfits, clowns, and con men, and Romney still can’t get to 30%. As Jon Chait recently noted, “I don’t see how Republicans could be making this any more plain. They do not want to nominate Mitt Romney.”

If I had to put money on the race, I’d say Romney gets the party’s nod anyway, only because there’s no plausible alternative. But when was the last time the Republican Party went into a general election with a nominee so much of the party simply didn’t like?

Steve Benen

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.