Trump and Cruz Turn Their Backs on Ronald Reagan by Geoff Colvin @FortuneMagazine May 4, 2016, 11:13 AM EDT E-mail Tweet Facebook Linkedin Share icons Remember Ronald Reagan’s commandment? “Thou shalt not speak ill of another Republican.” What innocent days those now seem. On Tuesday, the Republican Party approached self-immolation, though that sounds rather final, and we surely have not come to the end of the story. The leadership angle is that the two leading Republican candidates, striving for the world’s most important leadership job on the morning of the critical Indiana primary, abandoned all pretense of behaving like leaders. It can only be bad, very bad, for both of them and for the party’s chances in November. The spectacle began with Donald Trump saying on Fox News that Ted Cruz’s father was with President Kennedy’s assassin shortly before he was killed: “His father was with Lee Harvey Oswald prior to Oswald’s being — you know, shot.” You hadn’t heard? Well, unlike Trump, you apparently don’t get your news from the National Enquirer, which recently published that accusation with accompanying photo. Sign up for Power Sheet, Fortune’s daily morning newsletter on leaders and leadership. Cruz, knowing that a loss in Indiana would doom his candidacy, snapped and vented his deepest views about his opponent, which is almost always a mistake. He called Trump “a pathological liar. He doesn’t know the difference between truth and lies. He lies practically every word that comes out of his mouth.” He went on to describe Trump as “utterly amoral,” “a serial philanderer,” and “a narcissist.” Trump responded with a statement saying “I have watched Lyin’ Ted become more and more unhinged as he is unable to react under the pressure and stress of losing.” Forgive me, but these are eight-year-olds. The logical next step was for them to start wrestling and bite each other. To state the painfully obvious, this is not how leaders behave. It’s pretty much the opposite. Voters’ memories (and the video) of them acting like snippy brats won’t go away, and the things they said cannot be taken back or glossed over. Any hope of uniting the party behind Trump, now that his victory on Tuesday virtually assures him the nomination, is gone. Cruz attracted a substantial following, but now, having quit the race, it would seem impossible for him ever to endorse Trump. After all the incredible twists and turns in this race, the biggest reality hasn’t changed: Hillary Clinton is the most likely next president, just as she was a year ago. I’d be crazy to make any confident predictions, but it’s hard to imagine how the wisdom of Reagan’s commandment could have been demonstrated more dramatically than it was on Tuesday.