Republican senators in the U.S. Congress signaled on Thursday that they were hesitant to embrace a call from President Donald Trump for sweeping changes to gun laws, including measures more typically backed by Democrats.

Trump shocked fellow Republicans on Wednesday when he threw his support behind a broad set of restrictions on gun sales in response to the Feb. 14 mass shooting at a high school in Parkland, Florida, that killed 17 people.

The White House is expected on Thursday to release a list of policy measures that Trump backs. The president was set to privately discuss the issue with families of mass shooting victims and law enforcement on Thursday.