First off, yes I am serious. Secondly, rioters were not dispersed in the area by police officers, not because Trump was going through, bit because they were causing problems. Had nothing to do with the peaceful protesters. Multiple witnesses prove that and so did the reports from the officers themselves.
Do you think areas are not cordoned off before a president or dignitary comes through? It's called protocol and is done for the safety of a ranking official. Hell, even some celebrities are protected similarly.