Kentucky's U.S. Rep. Thomas Massie said attacks from fellow Republican President Donald Trump show he's worried about congressional opposition.

The Republican joked that Trump had "declared war" on him after he criticized the president for striking nuclear sites in Iran.

President Donald Trump and his political operation are working to unseat their first Republican incumbent: Kentucky Rep. Thomas Massie, who has drawn Trump's wrath by saying the president lacked the authority to attack Iran's nuclear sites without congressional approval and voted against his massive tax and spending cuts