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Tom Steyer, an American billionaire and environmentalist, called for the impeachment of the “mentally unstable” president. Addressing the public in a video advert this week, he said: “Donald Trump has brought us to the brink of nuclear war.” And he suggested that Mr Trump “is a clear and present danger, who's mentally unstable and armed with nuclear weapons, and the people in Congress do nothing.” The business tycoon added: “If that isn't a case for impeaching and removing a dangerous president, then what has our government become?

REUTERS - PA Donald Trump could be impeached over his war with North Korea

The Democratic mega-donor is spending what an aide says is "well over $10 million" on the national TV ad to help bring about Mr Trump’s impeachment. Mr Steyer explained that he is funding the effort “to demand that elected officials take a stand” on impeaching Trump. In an open letter, the billionaire goes on to say the president is simply lacking “fitness for office,” and says the question of impeachment has therefore “become a very real issue.” He wrote: "He has threatened to reduce aid for millions of American citizens in Puerto Rico who are struggling to survive without drinkable water or electricity -- a move that would be a total dereliction of his duty.

REUTERS The US President has brought America to the "brink" of nuclear war with North Korea

RODONG North Korea ramped up its missile program

"And every day, Americans are left bracing for a Twitter screed that could set off a nuclear war. These actions represent systemic attacks on our nation's future." READ MORE: Will Donald Trump start World War 3 with Kim Jong-un? The ads are running on broadcast stations in New York and California and nationally on cable television. And the calls for Mr Trump's impeachment comes as his war of words with North Korean despot Kim Jong-Un seemed to reach new highs this week

North Korea stages anti-US rally in battle with Donald Trump Mon, September 25, 2017 Tens of thousands of Pyongyang residents were gathered in the capital's Kim Il-Sung Square to laud leader Kim Jong-Un's denunciation of US President Donald Trump. Play slideshow AFP/Getty Images 1 of 12 Students march during a mass rally on Kim Il-Sung sqaure in Pyongyang