Three of the four Republican presidential candidates are addressing a major conservative gathering in Washington, giving them a high-profile stage to reshape their messages at a moment of uncertainty in the contest.

Former Sen. Rick Santorum rocked the Republican world this week by winning caucuses in Colorado and Minnesota, plus a nonbinding primary in Missouri.

His victories have raised new questions about Mitt Romney's ability to inspire conservatives, and about Newt Gingrich's claim to be the top alternative to Romney.

Santorum, Romney and Gingrich will separately address the annual Conservative Political Action Conference today. Rep. Ron Paul, whose libertarian leanings put him at odds with some mainstream conservatives, does not plan to attend.