But it is not Sen. Kennedy to whom we should be comparing RFK Jr., but rather Sen. Eugene McCarthy, the quixotic anti-war candidate who was able to expose the vulnerability of President Lyndon Johnson.

President Biden's handlers may be acting as though they don't consider RFK Jr. a credible threat, but that's exactly what it is – acting. They know that their octogenarian candidate has dangerously low favorability numbers, an arrogance perhaps not seen in Washington since LBJ retired to his Texas ranch, and as many putative supporters in his party as Julius Caesar had assassins.

Meanwhile, Kennedy comes from a beloved political family, yet at the same time is a fierce outsider. That is a combination rarely seen in a candidate and gives him at least the potential to achieve enough success to demonstrate to Democrat donors and primary voters that Biden is the emperor with no clothes.

So far, Kennedy has barely edged into the low 20s in polling, and currently he lags even lower in the RealClearPolitics average. But it's still early. At this point in 1968, LBJ seemed untouchable to the establishment media and the political class. Gene McCarthy, however, recognized that the nation was at a tipping point. And though he failed to capitalize, his campaign was the beginning of a new era of grassroots politics.

As described by PBS in an article for "The American Experience":

He didn't win the White House. He didn't even win his own party's nomination. But in 1968 Eugene McCarthy revealed major divisions among Democrats, changing the political landscape in a way few American politicians ever have.