Kansas’ two Republican U.S. senators worry about the precedent set by President Donald Trump’s declaration of a national emergency at the border with Mexico to secure more money for a wall.

Sens. Jerry Moran and Pat Roberts said Saturday that they are concerned that a future president could use a similar declaration to impose policies that Congress has not authorized. The White House has said $6.1 billion will be redirected to the wall.

But the senators said they are still studying the question of how much authority the president has under the U.S. Constitution to make such a move.

Moran said: “I’m worried that if it gets used this time, what’s the next instance in which it becomes used?”

Roberts said he worries about “government by fiat” in the future.