World leaders know much of what Donald Trump says “is untrue”, a senior Republican senator has said in an astonishing attack on the US President.

Bob Corker, the chairman of the Senate Foreign Relations Committee, said that Mr Trump’s presidency would be remembered for the “debasement” of the country.

He said that Mr Trump’s “constant non-truth telling” means he is lowering the office of the presidency and failing to be a role model for children.

Mr Corker also said he would not support Mr Trump if he ran for the White House again and declined to say he trusted the President with nuclear weapons.

The outburst marks the most heated attack by a Republican Senator on Mr Trump since he entered office after winning the election as the party's candidate.

It came just hours before Mr Trump was due to sit down with Republican senators to discuss his tax cut plans amid hopes a new law can be passed by Christmas.