"US Homeland Security tests response to possible mass exodus from Cuba"

Homeland Security conducted test exercises to prepare against a possible influx of Cubans. Call me crazy, they are worried about a possible influx similar to Mariel(125,000), but they are not concerned with the 15-20 million already here in the U. S. illegally? Why no test exercises on the border? Why such concern over POSSIBLE Cubans, but many here in the U.S. who are anti-U.S. and who have ties to terrorist nations are not on the CONCERN list?