When Nathan calls the President a "Damn intern-humping liberal", the writer's were referring to the real life President of the United States at the time, liberal democrat Bill Clinton, who famously was having sexual relations with intern Monica Lewinsky.
The "don't bite the guy's ear" remark by Frank refers to a famous boxing event two years prior to the airing of the episode, where renounced boxer Mike Tyson bite off a large part of one of boxer Evander Holyfield's ears.