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(CNN) -- If Newt Gingrich can't win Alabama and Mississippi, where can he win? The former House speaker fell short in the heart of Dixie on Tuesday, and it's not clear where he goes from here.
Approaching the halfway mark of the primary season, Gingrich has finished first in a grand total of two states: South Carolina and his home state of Georgia.
Geographically, bright red Alabama and Mississippi were virtual home turf for the former speaker -- two must-win states for him to at least claim the title of regional powerhouse.
Compared to South Carolina and Georgia, however, there was a clear, critical decline in Gingrich's support among several key groups on Tuesday.
Among self-described very conservative voters, Gingrich won 33% of the vote in Mississippi and 37% in Alabama. In South Carolina and Georgia, he won 48% and 53%.
Among evangelical or born-again voters, Gingrich won 30% of the vote in Mississippi and 31% in Alabama. In South Carolina and Georgia, he won 44% and 50%.
Among strong tea party supporters, Gingrich won 34% of the vote in Mississippi and 38% in Alabama. In South Carolina and Georgia, he won 48% and 55%.
Similar declines among all three voting blocs occurred in comparison to the Florida Panhandle -- a traditional Deep South region. Gingrich narrowly won the Panhandle during the Sunshine State's January 31 primary, according to exit polls.
Last week, Gingrich spokesman R.C. Hammond said the former speaker had to win Alabama and Mississippi in order to remain viable. Gingrich later asserted that he's going on to the national convention in Tampa no matter what happens.
Bravado aside, at some point the money dries up and voters stop listening. For Gingrich, that point may have come Tuesday night.
"If (Gingrich) can't win in the South, he needs to go," said Erick Erickson, editor-in-chief of the conservative RedState.org.
If Gingrich does go, Santorum will get the one-on-one challenge to Mitt Romney he's been all but pleading for. Romney told CNN Tuesday afternoon that Santorum is facing a "desperate end" to his campaign. Santorum's big wins on Tuesday night indicate that end is anything but nigh.
"It's just the beginning," Santorum spokesman Hogan Gidley said.
"This is a grassroots campaign for president," Santorum told a group of supporters in Louisiana Tuesday night. It's managing to "defy the odds day in and day out."
This race has now become an arduous delegate slog. The first man to claw his way to a bare majority of 1,144 wins. Heading into Tuesday, Romney had 459 delegates, Santorum had 203, and Gingrich had 118, according to CNN estimates. Ron Paul trailed badly, with 66 delegates.
Prior to Tuesday, Romney needed to win roughly 48% of the remaining delegates to go over the top. Santorum needed about 66% of the remaining delegates, and Gingrich needed 72%.
Given the calendar and the GOP's rules regarding the proportional allocation of delegates, it's tough to see a scenario under which anyone overtakes Romney. Santorum, Romney, and Gingrich each won roughly a third of the combined delegates at stake in Mississippi and Alabama.
Realistically, the name of the game for Santorum -- and Gingrich if he goes on -- is to prevent Romney from hitting the 1,144-delegate mark and push for a contested convention when the Republicans meet in Tampa in August.
Can it be done? Most analysts still expect Romney to eventually seal the deal in May or June, but the GOP's conservative base continues, on the whole, to be remarkably resistant to calls to fall in line behind the frontrunner.
"If we go to a convention, we would be signaling our doom in terms of replacing President Obama," Romney told Fox News earlier this week. "That will not happen."
There hasn't been a seriously contested convention since Gerald Ford and Ronald Reagan battled down to the bitter end 36 years ago. The odds of another contested convention are long, but the game of presidential politics is anything but predictable.