I didn't downvote your parent comment, but I was preparing to send you a couple of links that educate you about what hearsay actually is, like https://www.law.c

I didn't downvote your parent comment, but I was preparing to send you a couple of links that educate you about what hearsay actually is, like https://www.law.cornell.edu/rules/fre/rule_801 https://www.law.cornell.edu/rules/fre/rule_801, https://www.law.cornell.edu/rules/fre/rule_802 https://www.law.cornell.edu/rules/fre/rule_802, and https://criminal.findlaw.com/criminal-procedure/hearsay-evidence.html https://criminal.findlaw.com/criminal-procedure/hearsay-evid... to correct what you mistakenly think hearsay is. In this case, Mattis is a witness and would be called to testify under oath, under penalty of perjury and subject to cross examination, about statements the president made to him. The president or other witnesses could dispute that, also under oath and subject to perjury charges/cross examination. If they conflict, as they often do, the judge or jury as the case may be decides the case on the merits. It would be hearsay if they called the biographer and asked him about Mattis's statement. Furthermore, hearsay is admissible evidence in a number of exceptions that are described in the links I gave you (including excited utterances or statements against interest which may apply here)