CHICAGO /Illinois/, August 20. /TASS/. US President Joe Biden has questioned the mental state of Donald Trump, the 45th head of state and Republican presidential candidate.

"His stability is in question," the politician said, commenting on Trump’s words that Biden was forced out of the presidential race by a coup.

Biden responded in the affirmative when asked if he was ready for a transfer of power.

At the Democratic National Convention, which is being hel August 19-22, US Vice President Kamala Harris is expected to formally agree to run for the nation's top office in the November elections. The US presidential election will be held on November 5.