On January 23, two days after South Carolina, it was Mitt 29, Newt 28, with Santorum dead last behind Ron Paul at 11 percent. Seventeen days later: Mitt 36, Santorum 20, Gingrich 20, with Senator Sweater Vest having gained another three points overnight. Two Not Romneys enter, one Not Romney leaves.

Or maybe two Not Romneys enter and two Not Romneys remain. For the first time in the campaign, the two sweetest words in the English language can be whispered with the slightest trace of plausibility: Brokered convention. Over to you, Sean Trende:

If this split continues — Romney in the West and Northeast, Gingrich in the South, and Santorum in the Midwest — we could easily find ourselves in a scenario where no candidate crosses the 1,144-delegate threshold by the time voting ends. Consider this: Right now, Romney barely has a majority of the delegates. If Gingrich successfully contests the winner-takes-all allocation in the Florida primary (based on the RNC’s rule against such a format before April), no one would have a majority of the delegates as of today…

In April, Gingrich would have a great chance in Texas, Maryland and Delaware (increasingly de facto Southern states in the GOP primary electorate), while Romney would receive large delegate hauls in Rhode Island, Connecticut and New York. Santorum would have primaries in Pennsylvania and Wisconsin.

In the end, we could end up in California in early June with no clear nominee. While that state is nominally winner-take-all for a whopping 172 delegates, in fact it allocates the overwhelming majority of those delegates by Congressional District. Who is voting in a Republican primary in Nancy Pelosi’s or Maxine Waters’ district? I honestly have no idea, but if they’re different from the voters in the Latino central valley districts, and if they’re different than the voters in Orange County, and if they’re different from the voters in the Sierra districts, we really could have a situation where the state doesn’t produce a winner for the GOP.

If this occurs, and Ron Paul wins around 100 delegates along the way, we have a situation where no candidate has more than 900 delegates, and three have more than 400. In that situation, no one would be able to lay claim to the mantle of presumptive nominee. The convention would eventually deadlock, and an outside candidate could emerge.

Philip Klein made the same point last night about a persistent northeast/midwest/south regional split among the candidates, and tried to game out how many delegates Romney would win if that split held through June. Answer: Slightly more than 1,000, which is 140 fewer than he needs to clinch the nomination. Looking waaaaay down the road, the obvious problem for convention brokers would be to come up with a ticket that somehow heals that regional divide. Presumably GOP leaders would be willing to overlook the northeast on the theory that they probably won’t beat Obama there anyway. Daniels/Barbour, then? Ryan/Rubio? The only limit is your imagination, my friends — plus, I guess, the extreme unlikelihood that both Santorum and Gingrich will slog on to Tampa even after it becomes clear that Romney will finish with many more delegates than they will, if not an outright majority.

Here’s DeMint this morning on CNN with a very mild case of brokered convention fever. Can you feel it?