Trump’s $5,000 promise could cost $1.38 trillion. Here’s the big question: where would the money come from?

President Donald Trump has promised $5,000 to every American adult if Republicans retain control of the House of Representatives and the Senate in November's midterm elections.

The pledge has raised questions about its legality, its cost and where the money would come from.

Federal law prohibits offering payments in exchange for votes and separately restricts promises of federally funded benefits in return for political support.

Trump's offer would appear to skirt these prohibitions because it is more in the nature of a campaign promise and would apply to all adult Americans regardless of how they voted.