The non-monarch told U.S. troops stationed in Japan Tuesday that he was prepared to send “more than the National Guard” to American cities to safeguard and enforce his immigration agenda—a threat that could apparently involve any branch of America’s armed forces.

Speaking with reporters aboard Air Force One on his way to South Korea hours later, Trump clarified that he would do whatever is “necessary” to tackle crime, even if that meant ordering the U.S. military onto American soil.

“I would do that if it was necessary, if it was necessary I’d do that, but it hasn’t been necessary,” Trump said on the plane. “We’re doing a great job without that—is necessary. As you know, I’m allowed to do that.

“And I’d be allowed to do whatever I want, but we haven’t chosen to do that,” he continued. “And the courts wouldn’t get involved. Nobody would get involved. And I can send the Army, Navy, Air Force, Marines. I can send anybody I wanted.”

The president is typically prohibited from leveraging the U.S. military for domestic law enforcement purposes under the Posse Comitatus Act, though one law stands as the major exception to that rule. Trump could use troops to handle domestic issues if he invoked the Insurrection Act, but doing so would require a state of emergency.

The legal loophole has been used by 17 presidents but has not been invoked since 1992, when President George H.W. Bush used it to subdue riots in Los Angeles after the local police force brutalized Rodney King.