When the President of the United States announces that he plans to attend a conference, you, the manager of the conference site, will lose much of the control you usually have.  The success of the conference will be credited to you only in part.  Its failure may be your undoing. 

Typical security is not enough.  Even enhanced security is not enough.  The Secret Service will take charge and will dictate (in a non-dictatorial way*) exactly what it will do and exactly what is required from local sources.  The security chief of the conference center will become little more than an answer man/woman.

Downtown traffic will probably be diverted for a time, and the local populace will grouse about the discomfort.  Politicians will feel heat.  Those who side with the President will stand tall in defense.  Those in the other party will point out excesses.

Lodging requirements, beyond those of the presidential entourage itself (discussed in my previous entry), will mushroom as the Press, protestors, and seekers-of-the-spotlight will converge from all sides, whether related to the topic of the conference or not.  If the conference is on a hot topic, expect hordes.