The exact meaning of endorse can depend upon its context. For example:
"I endorse her candidacy." — support for a candidate
"I endorse the committee's recommendations." — support an idea
"She is paid a million dollars a year to endorse the company's products." — publicly support in return for payment
"She endorsed and deposited the check." — approved placing funds into a bank account by writing something like "for deposit" and signing the back of a check
Acting, therefore, in the defense of our own security and of the entire Western Hemisphere, and under the authority entrusted me by the Constitution as endorsed by the resolution of Congress, I have directed that the following initial steps be taken immediately.
There are no more uses of "endorse" in Killing Kennedy.