At 1:26 you will see the one Congressman lean away from a protestor who is cleary shouting at the Congressman. Ahead of the Congressman and just before the incident, a man is seen clearly taking a video of the protestor involved.
So the Congressman needs to prove his point since a member of his entourage was taking a video of the protestor.
The fact that he got sprayed with saliva from the man shouting, clearly shows it was not an act of "spitting" on the Congressman given that the woman police officer was right there, witnessed it and nothing was done.
Take note that the Congressman got another officer to what looks as if he wants him to make an arrest.