TOWN AND COUNTRY, Mo. (AP) — It's caucus day for Missouri Republicans, and Rick Santorum is shaking hands and imploring people outside St. Louis to support him.Santorum won Missouri's nonbinding primary last month, and Saturday he's the only candidate visiting caucus sites. Mitt Romney and Ron Paul campaigned in the state earlier in the week.Saturday's caucuses are nonbinding, but Santorum, Romney and Paul are hoping to advance a slate of backers to the next step.Republicans in nearly 140 local caucuses will elect more than 2,000 delegates to next month's district conventions. The district meetings will select delegates to the state's June convention. That's where the 52 delegates to the national convention will be chosen and bound to one of the four candidates vying for the Republican nomination.Newt Gingrich skipped campaigning in Missouri.