Where does the Republican nomination contest go from here? There are basically three paths remaining for a candidate to get to the 1,144 delegates it takes to clinch the nomination:

Long slog. By now, there are clear patterns of support for both Mitt Romney and Rick Santorum. If groups in the remaining states continue voting the way those groups have voted so far, it’s possible to project out the rest of the calendar. Plug in the delegate selection rules, and what you get is Romney wrapping things up pretty easily, but not until late May or June. I suppose I should add an improbably variation here in which somehow Newt Gingrich has yet another surge and it becomes Romney vs. Gingrich, in which case the long slog is much easier for Romney.

Stampede to Romney. Republican politicians, Republican-aligned interest group leaders, and other high-profile Republicans decide that Romney is the certain nominee and that the long slog isn’t in anyone’s interest. This works two ways. First, by publicly shifting their support to Romney, they change the information environment for voters in the next rounds of primaries and caucuses, thus helping Romney directly. At the same time, they exert what pressure they can on Santorum (and, I suppose, Gingrich) to accept reality and drop out. Romney then runs the table easily, beating Ron Paul by large margins in the remaining states.

Stampede to Santorum. Very, very, unlikely. We’ve already seen that given the choice, most high-profile conservatives would rather stay neutral than support Rick Santorum. It’s difficult to think of why they might hop aboard his bandwagon now. But it’s worse than that for Santorum; he’s already getting the votes of those who would be most influenced by high-profile conservatives. What he needs is to expand his appeal, which would presumably take an even larger inflow of resources. The math is certainly there for Santorum to win if he runs the table on the remaining primaries and caucuses; it’s just that there’s absolutely no reason to believe he might do that.

A stampede to Romney is quite a bit more likely than a long slog. The candidates who were able to force a long slog — Hillary Clinton in 2008, Gary Hart in 1984, Ted Kennedy in 1980, Ronald Reagan in 1976, Hubert Humphrey in 1972 — all had a lot more going for them than Santorum, and it’s no coincidence that more of those are Democrats and it’s only happened once since 1984. So do pay attention to future projections based on voting trends so far, but remember that there are other factors involved, and most of them really favor Romney at this point.