ICE is a branch of what use to be the INS. On reorganization under Homeland Security they separated the functions. ICE appears to be the internal enforcement branch that goes out and makes the busts of illegals, tracks down the felons and so on. Basically the Law Enforcement side of immigration. Like the rest of the former INS, they are grossly understaffed to deal with the 20,000,000 or so illegals we have in the USA today.
We have allowed this problem to get so out of habd that they could likely triple the number of agents they have and still have trouble keeping up.
IMHO, this will result in thousands more Americans dying at the hands of terrorists.