"Delegates. It's as simple as that. They matter," Santorum said, after an early morning visit to a caucus site at the Westminster Christian Academy in St. Louis.
Mixed among his supporters at the school were dozens of people with Romney signs planning to challenge local Republican leaders trying to elect a slate of Santorum delegates.
Norman Baxter, 77, a retired corporate communications officer who is the Republican committeeman for the local township, is among those pushing the Santorum slate.
"I'm a conservative — a strong conservative — and I think Santorum represents a lot of the values that I think are very, very important to the survival of this country," Baxter said.
Romney maintains a big advantage in the race for Republican National Convention delegates, with 495 to Santorum's 252, but is still a ways away from the 1,144 needed for nomination.
Former House Speaker Newt Gingrich and Texas Rep. Ron Paul, both of whom swung through Illinois earlier in the week, are also on Tuesday's ballot. But Gingrich has turned most of his attention to Louisiana, which votes next Saturday.
Associated Press writers Jim Salter in Wildwood, Mo., contributed to this report.
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