Asked in an interview with the Sunday BBC program "The Andrew Marr Show" following the release of a book about the current US administration, May said she had no concerns about the mental health of the US President.
"When I deal with President Trump, what I see is somebody who is committed to ensuring that he is taking decisions in the best interests of the United States."
Journalist Michael Wolff, in the book, quotes Trump advisers who question the President's competence.
Earlier, US President Donald Trump said in his Twitter that all his life, one of his main qualities was mental stability and intelligence.
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According to him, it can be called not just "smart", but "genius."
Earlier, Donald Trump, in an interview with Forbes magazine, offered to compare his IQ with that of Secretary of State Rex Tillerson.