Someone asked me if I think any of Ted Cruz' rivals would jump on this. Well, definitely not Hillary. And I don't think Bernie would either. The only one who might is Trump. And even he would only do it as a last resort, meaning, if it appeared that Cruz was going to take the nomination away from him. But, Trump is expected to win the New York primary handily. After all, it's his home state. And he may be over the top on the delegate count quite soon, and long before the convention.
If he does, will the Republican establishment then get behind Trump? I don't think so. I don't see how they could after the things they said. It would seem very hypocritical- to me.
But, they may try some shenanigans at the convention, even if Trump has the delegates he needs.
And, if Hillary is the Democratic candidate, I could foresee prominent Republicans urging Republican voters to vote for her.
Do you remember 1972? There was an organization called Democrats for the Re-election of the President. I remember seeing the bumper stickers. So, we might see something like that.
But yes, if push comes to shove, I think Trump would use the question of Rafael Cruz being with Lee Harvey Oswald shortly before the JFK assassination to his advantage. Even just raising the question would do a lot of damage. It would raise concern. And presumably, Trump would demand that Cruz address it, that he issue a denial, if that's his position.
But, one would expect him to give a full accounting, right? That means establishing where his father was at the time; stating whether or not his father was involved with the CIA; and whether he knew Oswald at all. And whatever information he provided others would try to vet.
If Trump was willing to go after Obama on the "birther" issue, then I don't see why he wouldn't go after Cruz about this- if he has to. But again: ONLY if he has to. If he's got the nomination sewed up, he's going to want to mend fences with Cruz and try to win his support.
So, if this is going to become an issue in the campaign, it won't be for a while.