The partial allocation of delegates from Tuesday's voting states left Romney with 495 in The Associated Press count, out of the 1,144 needed to win the nomination. Santorum had 252, Gingrich 131 and Paul 48.
And while Santorum in particular challenges the mathematical projections, Romney is amassing delegates at a rate that puts him on track to clinch control of nomination before the convention next summer.
A senior Romney adviser, Jim Talent, said the campaign is where it needs to be. "We're really running against the delegate totals more than any of the others," Talent told CNN Wednesday.
Gingrich deputy campaign manager Vince Haley suggested the former House speaker was putting himself in position to compete at a brokered convention, saying Gingrich could "win a debate in this country over the course of the rest of this campaign."
It is rare for Alabama and Mississippi to play an important role in a Republican nominating campaign, but the 2012 race has gone on far longer than usual. Equally improbable was the decision by Santorum and Romney to spend time during the next few days in Puerto Rico.
The Romney-aligned super PAC is already advertising in Illinois in hopes of gaining an advantage there.
All three candidates, as well as the super PACs supporting each of them, ran television commercials in Tuesday's Southern states. As has been the case all year, Restore Our Future, which backs Romney, spent more than any of the others, putting down $1.3 million for television ads in Alabama and another $900,000 in Mississippi.
Associated Press writers Stephen Ohlemacher and Connie Cass in Washington contributed to this report.
- Jason Chaffetz: Mitt Romney is leaving door...
- 'I am Adam Lanza's Mother' author Liza Long...
- Miss New York chosen as Miss America 2015
- Feds chase treasure hunter turned fugitive
- Gamers use police hoax to lash out at opponents
- US wealth gap putting the squeeze on state...
- 24-year-old American in North Korea sentenced...
- Britain mourns aid worker slain by Islamic...
- Jason Chaffetz: Mitt Romney is leaving... 65
- Obama 'confident' of Islamic State... 19
- US wealth gap putting the squeeze on... 19
- US, Arab allies committed to fighting... 15
- Here's how U.S. churches are changing... 15
- Ted Cruz was booed off stage for... 14
- Utah's Gov. Gary Herbert eyes more... 11
- Americans link violence with Muslims,... 9