"It's important that the great majority of Americans don't see an increase in their tax share," he added.
Romney spent the day in Massachusetts after sleeping at home for the first time in weeks, a result of a nominating campaign that has gone on longer than any in recent years.
Santorum campaigned in Mississippi and in Kansas, which holds caucuses next Saturday with 40 delegates at stake. Wyoming, with 12 delegates, is also on the calendar, as are the Virgin Islands, Guam and the Northern Marianna Islands, with 6 apiece. Mississippi and Alabama have primaries on Tuesday.
The former Pennsylvania senator won three Super Tuesday states, reviving his campaign after a recent string of setbacks, and he issued a fresh appeal for campaign funds to compete with Romney.
"We've proven we can win this race. ... I think this is because Americans are looking for a blue-collar Reagan conservative — not a Massachusetts moderate," the appeal said.
Next Tuesday's calendar runs from primaries in Alabama, 47 delegates, and Mississippi, 37 delegates, to caucuses in Hawaii, 17, and American Samoa, 6.
Santorum urged Mississippi Republicans to vote for him and, in essence, drive Gingrich from the race.
"If you deliver a victory for us on Tuesday, you will make this a two-person race," Santorum said at a small business in Tupelo, Miss. "And once it's a two-person race, the conservative will be the nominee. You can change it all, Mississippi."
The Romney campaign's decision to begin advertising in Alabama suggested a competitive race, as did a private poll and Gingrich's decision to skip a trip to Kansas to focus his efforts on the Alabama and Mississippi primaries. A Gingrich aide said the former House speaker must win both next week to justify his place in the race.
In Montgomery, Ala., he criticized both Romney and Santorum. He said the former is a moderate in the mold of Bob Dole and John McCain, both of whom led the party to defeats in presidential elections.
As for Santorum, he said, "I am not going to Washington to be a good team member. I'm going to Washington to change Washington." That was a reference to the former senator's recent debate statement that he voted for President George W. Bush's No Child Left Behind Education bill even though he opposed it, because he wanted to help the GOP team.
Associated Press writers Kasie Hunt in Massachusetts, Steve Peoples in Kansas, Thomas Beaumont in Alabama, Philip Elliott and Erik Schelzig in Mississippi, and Stephen Ohlemacher in Washington contributed to this report.
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