US president Donald Trump and first lady Melania Trump speak at a National Day of Prayer service in the Rose Garden of the White House in Washington, DC, on 2 May 2019

California is threatening to leave Donald Trump off the 2020 ballot unless he publishes five years of income tax returns, just as the president is attempting to put a lid on the Mueller report that has dogged his presidency.

The threat from the blue state comes in the wake of attorney general William Barr's divisive testimony before the Senate Judiciary Committee on Wednesday, which has inspired a war of words on Capitol Hill and seen House speaker Nancy Pelosi brand America’s top legal official “a liar”.

The Democratic-led House is considering holding Mr Barr in contempt of Congress over misleading statements he made, his refusal to show up on Thursday to a planned hearing, and for failing to deliver the full Mueller report alongside underlying evidence to Congress.