The president's eloquence in Tucson spoke to the heart of America. And his appeal to our best instincts speaks for itself.

Just hours before, from the near-polar region, we heard the near-polar opposite. Sarah Palin's belated apologia was a sharp-edged affirmation of the worst in her brand of pit-bull politics.

While the president was pitch perfect, she was tone-deaf, characterizing criticism of her now infamous crosshairs visual on a congressional district map as a "blood libel." Does she have any idea what she’s talking about?—which, on the record, is a fair question. Surely she can’t equate her latest political difficulties with the suffering and death of hundreds of thousands of Jews across centuries in Europe who were falsely accused of ritually murdering Christian children? It’s an unspeakable comparison, but Palin used it.

Neither of America’s two great political parties should ever nominate someone like Sarah Palin.

The most charitable reaction is that she didn't know what the phrase meant. But she must have known that this speech on this day, which rightly belonged to the victims, their families, and the country, would come across as a calculated grab for the spotlight. Suddenly up on Facebook popped her in-your-face defiance, which only entrenches her status as a factional figure. She could have reached out beyond the narrow confines of her base toward mainstream America by simply saying that while she didn’t believe the crosshairs on Gabby Giffords’ district had caused the shooting, on reflection—and because debate can be both vigorous and civil—she was sorry she’d ever approved the visual. That would have resonated with the moment—and it could have led people to think of her in a different way, and perhaps even to see her as a serious person.

The intellectual argument Palin offered up, if you can call it that, was equally unworthy. She distorted the meaning of a quote from Ronald Reagan, with whom she customarily and unconvincingly equates herself. Reagan insisted that lawbreakers are "accountable" for their actions—rejecting "the idea that society is guilty rather than the lawbreaker." Reagan’s point was that the wider society—its climate and its shortcomings—can't excuse a criminal. But that obviously doesn’t mean that a riven society can’t push an offender to the wall, or enable him to rationalize a crime—which is exactly what Palin twisted Reagan’s comment to say. "Deeds begin and end with the criminals who commit them," she said.

That may or may not be true in this case. But it’s plainly false as a categorical matter. What about those whose extremism inspires crimes—from 9/11 and the Oklahoma City bombing to the killing of Dr. Martin Luther King Jr.? I certainly don’t favor a speech police, but political leaders, especially those at the highest levels, have a duty to police their own invective. Words do have power—and whether or not it happened in Tucson, they can spur the fanatical or the deranged to the most heinous acts. Once you start flourishing M-16s at a political event, you have already begun to break the bounds of metaphor.

Palin fully revealed the ugly nature of her politics when she arraigned her critics as "those who embrace evil and call it good." This is a dangerously Manichean vision of public life; why can’t she just say her opponents are wrong? I've had intense exchanges with conservatives over the years; I sometimes get exasperated and heated, and so do they. But I don’t see them as evil—and I’ve never said it. A figure like Palin, who commands the national stage and a fervent following, should be cautious in how she characterizes opponents or different policies and points of view.

Sadly, she disdains that standard of basic decency—never more so than with her speech this week. Tongue in cheek, I used to endorse her for the Republican presidential nomination in 2012, knowing she would be a sure loser in the general election. But I can’t joke about her anymore; I retract the endorsement because neither of America’s two great political parties should ever nominate someone like Sarah Palin.

On Wednesday, Barack Obama bound up the hurts, touched our souls, and lifted our hopes. As he has before, he rose to the occasion with a magnificent grace.

Listen to his call to a more perfect union, and then listen to the recriminations of Sarah Palin—and we know why he’s president and she never will be.