The Republican presidential race isn’t even half over.

Republican presidential candidate and former Massachusetts governor Mitt Romney visits a campaign headquarters Jan. 19 in Charleston, S.C. (Joe Raedle/Getty Images)

Which means there is a long way to go.

At the same time, the states that have voted so far have given us a pretty good idea about where each candidate’s strengths lie — Rick Santorum in Southern and Midwestern states and among more conservative voters, and Romney in the Northeast and West and among more affluent voters, etc.

With that in mind, we thought it worthwhile to take a look at just how Romney gets to that magical number: 1,144 delegates.

(We focus on Romney because it’s virtually impossible for Santorum to get there; he would need to win 70 percent of the remaining delegates, which means he is playing to keep Romney from winning the nomination before the convention.)

The first thing we know: It will take a long time.

Because Texas and California (total: 327 delegates) don’t vote until May 29 and June 5, respectively, the calendar is heavily back-loaded, and it is impossible for Romney to get to 1,144 delegates until May 22, when Arkansas and Kentucky hold their primaries.

That’s assuming, of course, that Romney wins every delegate between now and then, which won’t happen.

If his opponents stay in the race, Romney will probably be looking to close out the nomination in Texas on May 29 or, much more likely, in California and four other states on June 5.

Romney would have to win 75 percent of the delegates between now and Texas to close out the race on May 29. June 5, meanwhile, is a veritable treasure trove of delegates for him, with California and New Jersey handing out 222 delegates. Those states should be Romney territory.

Second: It’s not really winner take all.

Once the calendar turns to April, party rules allow states to allocate their delegates on a winner-take-all basis.

That said, very few states actually award all of their delegates to the winner of the statewide vote. In fact, that is only the case in the District of Columbia, Delaware and Utah. The total number of delegates available in those three states: 76 delegates. (More on how each state awards its delegates here.)

Most of the states that are winner take all allocate most of their delegates, three at a time, to the winner of each congressional district. That means, if the candidates split the congressional districts evenly, they split the delegates evenly as well.

This is the case in Maryland, Wisconsin, Indiana, California and New Jersey and effectively the case in Pennsylvania and West Virginia, where delegates are directly elected by voters (total: 450 delegates).

And even if you combine these states with the true winner-take-all states, it doesn’t even comprise half the delegates that remain.

In other words, this is still a pretty proportional process, which can draw things out a little more.

. . .Which brings us to No. 3: The second half of the calendar is much friendlier to Romney.

As we’ve written before, Romney hasn’t lost a primary outside the South, and his caucus losses have been relegated to the middle of the country.

Why does that matter? Because the second half of the delegate calendar is dominated by primaries held outside the South, and relatively few Midwestern states remain.

Next month alone, 287 of the 329 delegates will be handed out in the Northeast. And to close out the race, Romney has some very friendly states where he will either be guaranteed a victory (Utah) or a heavy favorite (California and New Jersey).

If Santorum wants to prevent Romney from reaching 1,144 delegates, he’s going to have to start pulling some upsets in the Northeast and the West. He can’t just rely on his bread-and-butter regions and expect to hold Romney below that magic number.

Assuming Romney does well in California, New Jersey, Utah and the Northeastern states in April, the onus will be on Santorum to do well in a few states in particular.

In April, he probably needs to notch wins in Wisconsin’s primary on April 3 and his home state of Pennsylvania on April 24. On the latter date, he also needs to prevent what could be a bloodbath in New York, where Romney could win the vast majority of the delegates if he clears 50 percent of the vote (the threshold at which that state awards its 34 statewide delegates on a winner-take-all basis).

Santorum then needs to rack up as many delegates as possible in early May in conservative states like Indiana, North Carolina, West Virginia, Nebraska, Arkansas and Kentucky before the big states close out the process.

That’s a lot of states that could be friendly to Santorum. Unfortunately for him, most of those states are proportional and none are big delegate prizes. So the idea that he’s going to net a lot of delegates in those states seems far-fetched.

That’s also the case in Santorum’s one big state: Texas. All of its delegates are awarded proportionally by both the statewide vote and by congressional district. So unlike California, for example, even if Santorum sweeps the state and wins by a huge margin, he won’t win a huge delegate prize.

Which means Romney will almost definitely have a chance to close out the race on June 5, when California holds its primary.

And barring some kind of game-changing event, he should have a pretty good chance to do it then.