Yale professor Dr Bandy X Lee, an expert on violence, believes that President Donald Trump is 'unraveling' and that he poses a 'public health risk' by being in office

A Yale University psychiatry professor has met with lawmakers to discuss President Donald Trump's mental health.

Dr Bandy X Lee, an expert on violence, believes that the president is 'unraveling' and that he poses a 'public health risk' by being in office.

Lee gave a presentation in Congress on why Trump's presidency was an 'emergency' to a group of Democrats and one Republican senator during private meetings on December 5 and 6.

'From a medical perspective, when we see someone unraveling like this, it's an emergency,' Lee told the New York Daily News. 'We've never come so close in my career to this level of catastrophic violence that could be the end of humankind.'

She added that psychiatrists are prohibited from diagnosing from afar, but said Trump's behavior is worrying.

'He's very attracted to means of violence as a way of burnishing power,' Lee said, noting the threats and attacks he has made since becoming president.

The professor previously edited the book The Dangerous Case of Donald Trump: 27 Psychiatrists and Mental Health Experts Assess a President.

Lee gave a presentation on why Trump's presidency was an 'emergency' to a group of Democrats and one Republican lawmaker during private meetings on December 5 and 6. Pictured above, Trump with First Lady Melania Trump

Lee said lawmakers were 'enthusiastic' to speak with her and her colleagues last month, adding that their 'main concern' was getting Republicans to agree on Trump's behavior.

'What they were saying is that Republicans were also concerned [about Trump's mental health] — possibly equally concerned, but as to whether they would act, that was a different question,' she told the Daily News.

Earlier this week, several experts mentioned the 25th amendment after Trump tweeted about Kim Jong-un after the North Korean leader threatened a nuclear attack.

Trump wrote: 'Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!'

Richard Painter, a former ethics lawyer under President George W. Bush said 'This tweet alone is grounds for removal from office under the 25th Amendment'.

The Constitution's 25th Amendment created a system for replacing the president and vice president in case of death, removal, resignation or incapacitation.

Earlier this week, several experts mentioned the 25th amendment after Trump tweeted about Kim Jong-un after the North Korean leader threatened a nuclear attack

The amendment allows the Cabinet to remove a president if physical or mental health impairs him or her from performing the daily duties of the office.

It states that, if the vice president 'and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide' declare that the president is unable to perform his duties, the vice president will assume powers as an acting president.

The amendment was formed after the assassination of President John F Kennedy in 1963.

Press Secretary Sarah Huckabee Sanders defended Trump's tweet about Kim on Wednesday, saying Americans should be concerned with the North Korean leader's mental fitness.

'The president and the people of this country should be concerned about the mental fitness of the leader of North Korea,' Sanders said.

'He's made repeated threats, he's tested missiles time and time again for years, and this is a president who's not going to cower down and who's not going to be weak and is going to make sure that he does what he's promised to do and that is stand up and protect the American people,' she added.