It's one thing to remove a heckler from a hall where a candidate is making a speech, but to silence people at a parade is out of control. Who does Hillary really think she is? Hillary has her own private army, like it's any better that they wear trenchcoats and not brown shirts.
Simple solution. Ask them for their idenification as United States Secret Service agents. If they are USSS, they are way out of line. If they are not, you are well within your rights to tell them shut the #$%& up and get out of your face. Videotape everything.