Federal election standards "a very sensitive area with the states, too, so I’d urge caution in how you go about this," says Jeh Johnson.
Johnson touts first-ever mission statement in exit memo.
Forms applicants signed said information "will not be used by immigration enforcement."
Homeland Security secretary argues U.S. already has "deportation force" with ICE.
Deportations paused because of Hurricane Matthew but will resume "as soon as possible," Johnson says.
Johnson: "I'm not referring to anything presidential candidates say. But I have before called it out when I hear it."