There was an attempt on George Wallace in the 1972 campaign.
This time he was a running as a Democrat not an independent.
What has been forgotten is that Wallace had accumulated more delegates at the time of the attempt than any other candidate.
That is not to say that he would have gotten the nomination but Wallace was running a populist campaign to what was still the base of the Democrat Party at the time which was the blue collar worker middle class.
Yes, I left out Wallace because he really had no support outside of the Old South, so really wasn’t a ‘threat’ to anybody.
But it was interesting that when the election came he told Nixon he could have all his electoral votes if he needed them............