The shortfall underscored the advantage that Romney has maintained throughout the ups and downs of the turbulent nominating fight: his big financial and organizational advantages.
Both were brought to bear on Super Tuesday. Repeating a pattern seen throughout the contest, Romney vastly outspent Santorum on the television airwaves, strafing his chief rival with a relentless barrage of negative advertising.
Santorum sought to make Romney's spending and attack ads an issue — as Gingrich had in earlier states — but most voters did not seem as upset.
Party leaders and other insiders have grown increasingly concerned, however, about the toll the contentious nominating fight has taken on the GOP and its candidates, reflected in polls showing gains by President Obama and increasingly sour views of the GOP field. That played to Romney's benefit, as he continued to rack up endorsements from within the party establishment in recent days.
With a string of three wins — in Arizona, Michigan and Washington state — Romney increasingly sought to project an air of inevitability, hoping to hasten a close to the contest. His strategists, knowing he was sure to win the delegate count, insisted that was the chief arbiter of success Tuesday.
"More important than winning this state or that state is achieving the requisite number of delegates to achieve the nomination," Eric Fehrnstrom, a Romney advisor, told reporters Monday as the candidate flew between stops in Georgia and Ohio. "That's what our focus is."
But there were many ways to slice Tuesday's results and thus many ways for a candidate to claim victory and justify continuing to campaign, even if it becomes mathematically impossible for anyone but Romney to win the nomination outright.
So the race continues. Next up among the major contests are caucuses Saturday in Kansas, and on Tuesday, primaries in Alabama and Mississippi and caucuses in Hawaii.
Times staff writers John Hoeffel in Vinings, Ga., Seema Mehta in Steubenville, Ohio, and Maeve Reston in Boston contributed to this report.