ABC News weighs in.
Santorum's decision on Tuesday closed that window, although Newt Gingrich has vowed to stay in the race until the convention.
Romney still has to win an additional 483 delegates before he can technically claim the title of the 2012 Republican Presidential candidate.
So, how long until Romney reaches that point?
There's still a little more than month to go until the Romney campaign gets to that critical number. Mathematically, it can't happen until the end of May.
The next slate of primaries are scheduled for April 24th, when a total of 231 delegates will be up for grabs across five states. After that, the primary schedule picks up again, with Indiana, North Carolina and West Virginia holding their primaries on May 8th, followed by Oregon and Nebraska on the 15th, and Arkansas and Kentucky on the 22nd.
A total of 507 delegates will be at stake in those 12 contests.
With Newt Gingrich and Ron Paul still in the race, it's possible- even likely- that Romney will not win 100 percent of those 507 delegates. Gingrich has a solid chance of picking up a couple delegates in states like North Carolina, West Virginia and Arkansas.
Still- assuming that Gingrich and Paul don't experience a huge surge of momentum in the wake of Santorum's departure, Romney looks well poised to clinch the nomination by the end of May.
If he doesn't get there by the 22nd, Romney will almost certainly reached 1,144 by the 29th, when Texas holds their primary with 155 delegates at stake.http://abcnews.go.com/m/blogEntry?id=16111430