Trump posts picture of 'veto' hat on Truth Social

President Donald Trump on Tuesday night posted a photo of a red hat with the word "veto" on it, as exit polls showed Democrats had swept to power in Congress.

To pass laws, a piece of legislation must be approved by both chambers of Congress before it is sent to the president to be signed. The president has the power to veto a law. Overriding a presidential veto requires a two-thirds supermajority in both chambers.