John Bolton, former George W. Bush ambassador to the United Nations, served as a national security advisor for Trump from April 2018 to September 2019.

Trump repeatedly referred to him as Mike Bolton to aides and in public.

Michael Bolton is a famous singer.

Trump also called Apple CEO Tim Cook “Tim Apple,” Vice President Mike Pence “Mike Pounce,” and former Speaker of the House Paul Ryan “Ron.”

Newsweek – ‘Mike Bolton’: Donald Trump’s Relationship With His National Security Adviser Is So Distant That He Sometimes Can’t Remember His Name
The Week – Trump sometimes calls John Bolton ‘Mike’
CNN – Hear President Trump’s latest name flub
PBS – Trump fires national security adviser John Bolton