The decisive victory by Mitt Romney over Rick Santorum in today’s Illinois presidential primary proves everything and nothing — all at the same time.

Republican presidential candidate, former Massachusetts Gov. Mitt Romney (R) is given a tour of the Google Chicago headquarters by Google Vice President Jim Lecinski (2nd R) March 20, 2012 in Chicago, Illinois. (Photo by Chip Somodevilla/Getty Images)

And nothing in the sense that even Romney’s staunchest allies don’t expect him to pick up enough momentum to win the Louisiana’s caucuses set for Saturday, meaning that the “Romney can’t win the South” and “Romney can’t win conservatives over” storylines will linger as the calendar turns from March to April.

“Nothing impossible in Louisiana but Santorum [is] not likely to be closed out soon,” acknowledged Charlie Black, a longtime Republican campaign hand who is supporting Romney.

As we have written before, both Romney and Santorum have enough likely “wins” over the next two months of the nominating calendar to justify continuing on in the race.

April is perhaps Romney’s best potential month of the race with a series of Midwestern and Northeastern states set to vote; May looks promising for Santorum with the race turning back to the South and Plains.

Add to that calendar/geographic reality the fact that two-thirds of Illinois primary voters said they are comfortable with the race continuing on so that their preferred candidate can win and it seems entirely plausible that what happened in Illinois makes little difference as the race grinds forward.

Santorum and his surrogates will continue to make the case that the conservative win of the party still isn’t sold on Romney and by nominating him the GOP will be sacrificing their best chance at beating President Obama in the fall.

Romney and his side will argue that Santorum isn’t the true blue conservative he paints himself as and that he is ill equipped to win a fight with President Obama on the only issue most voters care about: the economy.

Overarching all of that spin is the cold, hard math.

There is little question that Santorum can’t overtake Romney in the delegate count and has only the longest of shots to reach the 1,144 delegates, which are needed to clinch the nomination. (Santorum’s take on where the delegate count stands currently is somewhat far fetched.)

And yet, as NBC’s “First Read” noted Tuesday morning, even if Romney won every single delegate available after today, he wouldn’t reach the magic 1,144 number until the May 29 primary. If he won 60 percent of the delegates, Romney wouldn’t get to the threshold number until the Utah primary on June 26.

What all that means is that the only way to “end” the race is for Santorum and Gingrich to bow to that delegate reality or for the establishment to try to, well, make them bow to that reality.

The first scenario — Santorum simply deciding to call it quits — seems very unlikely, particularly given that his decidedly uphill delegate path has been a reality since, at least, Super Tuesday and the former Pennsylvania senator continues to soldier on in the race.

The second scenario is slightly more likely although far from a sure thing. In truth, the major establishment figures of the Republican party have been very wary to wade into the “should this end now” argument for fear, wethinks, of pissing off the conservative/tea party base.

If you are, for example, Florida Sen. Marco Rubio why would you risk the negative blowback that could be directed at you if you step in and say “enough is enough”? You wouldn’t.

And so, the slog continues. Romney remains the all-but-certain winner but without the ability — at least so far — to land the single knockout blow he needs to convincingly end this race. Illinois didn’t change that. But in defense of the Prairie State, it’s hard to see any state playing that role at this point in the process.