If FFC wanted us to think about it, it would be in the historical context of the conversation taking place several years before the JFK assasination. Up to Nov. 22nd 1963 it may have been thought of as impossible (and unthinkable) to kill a President...especially one surrounded by secret service agents during motorcade, from a grassy knoll on a sunny day in Texas.

While in 1958 Tom is claiming getting close enough to Roth to kill him would be as unlikely as getting to the President, a 1970's (and beyond) audience knows that neither is impossible....if someone wants it done badly enough.

Personally, I think it's quite a clever bit of dialogue.

Apple

ps - and yes, Don Smitty I did understand your question. But I do not believe there was a hint in there that a few years later Michael Corleone would decide to eliminate JFK.