http://www.duhaime.org/LegalDictionary/S/Slander.aspx
The US Supreme Court defined slander as:
"... slander ... may be divided into five classes, as follows: (1.) Words falsely spoken of a person which impute to the party the commission of some criminal offence involving moral turpitude, for which the party, if the charge is true, may be indicted and punished. (2.) Words falsely spoken of a person which impute that the party is infected with some contagious disease, where, if the charge is true, it would exclude the party from society; or (3.) Defamatory words falsely spoken of a person, which impute to the party unfitness to perform the duties of an office or employment of profit, or the want of integrity in the discharge of the duties of such an office or employment. (4.) Defamatory words falsely spoken of a party which prejudice such party in his or her profession or trade. (5.) Defamatory words falsely spoken of a person, which, though not in themselves actionable, occasion the party special damage.
"Certain words, all admit, are in themselves actionable, because the natural consequence of what they impute to the party is damage, as if they import a charge that the party has been guilty of a criminal offence involving moral turpitude, or that the party is infected with a contagious distemper, or if they are prejudicial in a pecuniary sense to a person in office or to a person engaged as a livelihood in a profession or trade; but in all other cases the party who brings an action for words must show the damage he or she has suffered by the false speaking of the other party."

Sorry, Honestly haven't seen any SLANDER of POTUS or Speaker.