Donald Trump‘s decision to mock a rival by calling her “Pocahontas” could lead to his impeachment, a political historian has claimed.

The US President used the Native American icon’s name to refer to Senator Elizabeth Warren during a White House event honouring Navajo veterans, who helped the US Armed Forces to pass secret messages during the Second World War.

Ms Warren, a Democrat who claims to have Native American ancestry said she “really couldn’t believe” the comment.

Political historian Allan Lichtman who has authored The Case for Impeachment, said the comment form “part of an article of impeachment.”

He added that Abuse of Congress has previously been cited as grounds to remove a US president.

An 1868 article of impeachment against Mr Johnson – one of only two US Presidents who have been impeached – said he “used intemperate, inflammatory and scandalous harangues … and loud threats and bitter menaces … against Congress”.

Mr Lichtman told Newsweek that ”a fairly powerful” article of impeachment could be formed if such comments were combined with “very intemperate attacks” on the judiciary and freedom of the press.

Many have condemned Mr Trump’s use of “Pocahontas” to refer to Ms Warren.

Navajo National Council Delegate Amber Kanazbah Crotty, who said the comments represented “the latest example of systemic, deep-rooted ignorance of Native Americans”.

Ms Warren herself, told MSNBC: “This was supposed to be an event to honour heroes, people who put it all on the line for our country. It is deeply unfortunate that the president of the United States can’t even make it through a ceremony honouring these heroes without throwing out a racial slur.”

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Her fellow Massachusetts senator, Ed Markey, said: “What Mr Trump said about my partner, Senator Warren is a slur. It disparages the Native American war heroes, standing right beside the President, who risked their lives to protect his right to make such a disgusting comment.”

The White House dismissed the criticism. Asked if the word was racist, White House press secretary Sara Huckabee Sanders, said: “I don’t think that it is.”

She was then asked why the President would say something that was “offensive to many people while honouring the Navajo code talkers — genuine American heroes”.

She replied: “I think what most people find offensive is Senator Warren lying about her heritage to advance her career.”