Falsus in uno falsus in omnibus

                                 Latin  false in one thing false in everything

nothing more need be said

                           although he was curious what the name was of a person who follows a liar

Wikipedia he doesnt often utilise it:

                                   “The Washington Post said in January 2020 that (the Former) had made more than 16,241 false or misleading claims as president, an average of about 14.8 such statements per day. The Toronto Star which said that, as of June 2019, (the Former) had made 5,276 false statements since his inauguration.”

A liar is a liar is a liar

                       Shakespeare  Thank you

1449,  Monday,  20  12. 21

https://en.wikipedia.org/wiki/Veracity_of_statements_by_Donald_Trump#:~:text=The%20Washington%20Post%20said%20in,false%20statements%20since%20his%20inauguration.