A Republican senator has dramatically announced he would not seek re-election and eviscerated Donald Trump’s behaviour in the White House.

Jeff Flake attacked the US President's “reckless, outrageous and undignified” actions as a “danger to democracy” in an impassioned speech on the Senate floor.

The Senator from Arizona criticsed Mr Trump for “glorying in the things that divide us and calling fake things true and true things fake”.

And he urged other Republican congressmen to speak out, telling the White House: “Mr President, I will not be complicit or silent.”

The speech amounted to the strongest attack on Mr Trump from a sitting member of his own party and came just hours after another Republican Senator made public criticisms.

Mr Flake’s decision not to run for re-election next year is a victory for Steve Bannon, Mr Trump’s former senior adviser, who is seeking to oust incumbent senators.