William Kennedy Smith and Jean Kennedy Smith are the nephew and sister of President John. F. Kennedy and Sen. Robert F. Kennedy, who was assassinated on June 6, 1968.

On April 4, 1968, the day the Rev. Martin Luther King Jr. was shot and killed, Robert Kennedy was campaigning for the presidency in Indianapolis. Bobby conveyed the news of King’s death to a shattered, mostly black audience. He took pains to remind those whose first instinct may have been toward violence that President John F. Kennedy had also been shot and killed. Bobby went on, “What we need in the United States is not division; what we need in the United States is not hatred; what we need in the United States is not violence and lawlessness, but is love, and wisdom, and compassion toward one another, and a feeling of justice toward those who still suffer within our country, whether they be white or whether they be black.”

That speech has crystallized into the single most enduring portrait of Bobby’s candidacy. Because it was extemporaneous, it conveyed directly, and with raw emotion, his own vulnerability, his aspirations for his country and a deep compassion for the suffering of others. Bobby concluded his remarks that night by urging those listening to return home and say a prayer for our country and for our people. Those words mattered. While there were riots in cities across the nation that night, Indianapolis did not burn.

Donald Trump made a controversial comment about rival Hillary Clinton during a rally in Wilmington, N.C., August 9. Trump told the audience, “If she gets to pick her judges, nothing you can do,” adding: “Although the Second Amendment people, maybe there is, I don’t know.” (The Washington Post)

Today, almost 50 years later, words still matter. They shape who we are as a people and who we wish to be as a nation. In the white-hot cauldron of a presidential campaign, it is still the words delivered extemporaneously, off the cuff, in the raw pressure of the moment that matter most. They say most directly what is in a candidate’s heart. So it was with a real sense of sadness and revulsion that we listened to Donald Trump, the Republican nominee for president, as he referred to the options available to “Second Amendment people,” a remark widely, and we believe correctly, interpreted as a thinly veiled reference or “joke” about the possibility of political assassination.

Political violence is a terrible inherent risk to any free society. Dictators and strongmen like Vladimir Putin have an answer. They are surrounded and shielded by force at all times. They do not brook dissent. In democracies, we expect our leaders to be accessible and, by and large, they want to be. Inevitably, that makes them vulnerable and the loss of a leader at a crucial time impacts family, country and even the world, for generations. Anyone who loves politics, the open competition of ideas and public participation in a free society, knows that political violence is the greatest of all civic sins. It is not to be encouraged. It is not funny. It is not a joke.

By now, we have heard enough dark and offensive rhetoric from Trump to know that it reflects something fundamentally troubled, and troubling, about his candidacy. Trump’s remarks frequently, if not inevitably, spark outrage, which is followed by a clarification that, in lieu of an apology, seeks to attribute the dark undertones of his words to the listener’s twisted psyche. This fools no one. Whether you like what he is saying or, like a growing segment of the electorate, you reject it, it is easy to grasp Trump’s meaning from his words. But what to make of a candidate who directly appeals to violence, smears his opponents and publicly bullies a Gold Star family, a decorated prisoner of war and a reporter with a disability, among others? To borrow the words of Army Counsel Joseph Welch, directed at another dangerous demagogue: “Have you no sense of decency, sir, at long last? Have you left no sense of decency?”

The truth remains that words do matter, especially when it comes to presidential candidates. On that basis alone, Donald Trump is not qualified to be president of the United States.