Even if that was the guy's aim with the umbrella on Dealey Plaza, I can't see any credible relevance to the assassination.
I think he was just doing, as he said, some heckling of JFK.
This is from his testimony:
Mr. GENZMAN. Why were you carrying an umbrella that day?
Mr. WITT. Actually, I was going to use this umbrella to heckle the President's motorcade.
Mr. GENZMAN, How had you gotten this idea?
Mr. WITT. In a coffee break conversation someone had mentioned that the umbrella was a sore spot with the Kennedy family. Being a conservative-type fellow, I sort of placed him in the liberal camp and I was just going to kind of do a little heckling.
Mr. GENZMAN. Are you saying you were going to use the umbrella as a symbol for the purpose of heckling?
Mr. WITT. I think that would cover it.
The Kennedys - specifically Joe Sr. - were often accused of supporting the appeasement policies of Chamberlain. LBJ took a shot at them during his campaign. I think this was all that he was doing.
But too many conspiracists - not all - can't see any innocent acts in this. Everything for them has sinister purposes. It's a mindset, a worldview, a view of "the government" and "the CIA" and "the deep state" as being behind all sorts of things. Yes, sometimes that is true; but sometimes it's not.