Hosted by the Heritage Foundation and the American Enterprise Institute, the theme of tonight's Republican presidential debate is foreign policy and national security.The debate is being held at Constitution Hall in Washington, D.C.CNN is carrying the debate live at 8 p.m. EST.Participating candidates are: businessman Herman Cain, former Massachusetts Gov. Mitt Romney, Texas Gov. Rick Perry, former Speaker Newt Gingrich, Reps. Ron Paul (TX) and Michele Bachmann (MN), former Gov. Jon Huntsman, and former Sen. Rick Santorum.