Milwaukee County Sheriff David Clarke said Friday that President Donald Trump's vow to "destroy the vile, criminal" MS-13 street gang "has got to shock the hell out of them."

"It says to the leader of their gang, the leader of the free world, the president of the United States has you in his sights and he's gunning for you," Clarke told WABC Radio host Rita Cosby.

"When the federal government comes down on you, it comes down hard," he added. "I think they know that their days are numbered."

In a speech to law enforcement on Long Island in New York, Trump touted efforts by federal authorities to root out MS-13, which has killed as many as 20 people between January 2016 and April of this year.

Gang members also brutally massacred four young men in April in a park in Central Islip, N.Y.

"I have a simple message to today for every gang member and criminal alien that are threatening, so violently, our people," President Trump said. "We will find you, we will arrest you, we will jail you — and we will deport you."

Clarke told Cosby that because of Trump's speech, "I would imagine that many of them will vacate the area on their own."