Gingrich also took aim at Santorum, saying his support for earmarks and other spending projects while in Congress had alienated voters from the Republican party in 2006. Republicans lost both the House and Senate that year, and Santorum lost re-election to the Senate by an 18-point margin.
"This is somebody who on a number of occasions had Washington change him — he admits it and he says it's a team sport. You had to go along to get along," Gingrich said of Santorum.
Romney had no campaign appearances Sunday but was scheduled to attend an event Monday night in Alabama.
Meanwhile, this campaign and an allied independent group were far outpacing his rivals on the air.
Restore Our Future, a super PAC run by former Romney advisers, was spending $1.42 million on ads in Alabama and $973,000 in Mississippi. The Romney campaign boosted its television ad spending from $165,000 to $233,000 in Alabama.
Gingrich and Santorum were also benefiting from air support from well-heeled outside groups.
The Gingrich campaign was running about $125,000 in ads in Alabama and $83,000 in Mississippi, while the pro-Gingrich super PAC Winning Our Future was spending $413,000 on ads in Alabama and $250,000 in Mississippi.
Santorum had only a nominal presence on the air in both states. But the Red White and Blue fund, his allied super PAC, was spending $275,000 on ads in Alabama and $235,000 in Mississippi.
Wins in the U.S. territories Guam, the Virgin Islands and the Northern Mariana Islands along with Wyoming helped Romney significantly pad his delegate lead in the race. The Associated Press calculates that Romney now has 454 delegates compared with 217 for Santorum, 107 for Gingrich and 47 for Texas Rep. Ron Paul.
A candidate must win 1,144 delegates to clinch the Republican presidential nomination at the national convention.
Elliott reported from Tupelo, Miss. Associated Press reporter Stephen Ohlemacher contributed to this report.
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