BOCA RATON -- In a private meeting with Richard Nixon in 1990, the former president warned Bill McCollum that America's next big threat would come from Muslim extremists. McCollum, a former Orlando-area congressman who is a candidate for the U.S. Senate seat held by Democrat Bob Graham, recounted that conversation to a Thursday gathering of the Boca Raton Republican Club, where there was much talk of America's war with Iraq. The club is planning a "Support America Rally" on April 10 at the South Palm Beach County Civic Center, at 16700 Jog Road west of Delray Beach. The 7 p.m....