Donald Trump has been warned by fiscal hawks within his own party in the US Senate that he must “get serious” about cutting government spending and reducing the national debt or else they will block the passage of his signature tax-cutting legislation known as the “big beautiful bill”.

Ron Johnson, the Republican senator from Wisconsin who rose to prominence as a fiscal hardliner with the Tea party movement, issued the warning to the president on Sunday. Asked by CNN’s State of the Union whether his faction had the numbers to halt the bill, he replied: “I think we have enough to stop the process until the president gets serious about spending reduction and reducing the deficit.”