By contrast, when Hillary Clinton, the Democratic Party's presumptive presidential nominee and a longtime champion of abortion rights, called a fetus an "unborn person," she really should have known better. Her stumble, like Trump's, exposed a taboo that facilitates blinkered thinking about abortion.
Trump, who used to describe himself as "pro-choice," says he changed his mind over the years as a result of "stories" from friends and acquaintances. Yet there seems to be no public record of this conversion prior to a speech that Trump gave at the Conservative Political Action Conference in February 2011, when he was considering a run for the Republican presidential nomination.
Even if we assume that Trump's switch from pro-choice to pro-life was sincere as well as politically convenient, it's clear he did not familiarize himself with the movement he was joining. Had he done so, he would have anticipated the barrage of criticism he provoked from his ostensible allies by saying, during an interview with MSNBC's Chris Matthews last week, that "there has to be some form of punishment" for women who defy the abortion ban he favors.
"The National Right to Life Committee unequivocally opposes the killing of innocent unborn children and works unceasingly to have them protected in law," the group's president, Carol Tobias, said in response to Trump's comments. "Unborn children and their mothers are victims in an abortion. In adopting statutes prohibiting the performance of abortions, National Right to Life has long opposed the imposition of penalties on the woman on whom an abortion is attempted or performed. Rather, penalties should be imposed against any abortionist who would take the life of an unborn child in defiance of statutes prohibiting abortions."
Trump immediately and uncharacteristically fell in line, parroting that position in a statement issued the same evening. But his confusion is understandable: If abortion is murder, why should women who hire professional killers to do away with their "innocent unborn children" get a pass?
Perhaps the rationale for exempting women who obtain abortions from criminal liability is that they do not understand the nature of their actions. But the same excuse applies to abortionists, since they generally do not think of their work as baby killing.
What is the proper legal response when the pregnant woman and the abortionist are the same person? If a woman takes a drug that induces a miscarriage, does she deserve sympathy or condemnation?
It is understandable that pro-life activists do not want to appear callous by holding women who obtain abortions responsible for their actions. But they can avoid that unpopular position only by denying the moral agency of pregnant women, as if the same hormones that cause morning sickness erase the ability to choose between good and evil.
If the pro-life movement does not want us to think about what is going on inside a pregnant woman's brain, the pro-choice movement does not want us to think about what is going on inside her uterus. Here is where Clinton erred on Sunday, when she declared, during an appearance on "Meet the Press," that "the unborn person doesn't have constitutional rights."
That statement is legally nonsensical, since a "person" has constitutional rights by definition. In fact, the abortion debate largely comes down to the question of whether -- and when -- a fetus counts as a person.
Clinton's comment is also rhetorically problematic, conceding the fetus's humanity while denying its right to life. An Illinois pro-choice activist complained on Twitter that Clinton's formulation "further stigmatizes #abortion."
For those who see abortion as murder, of course, the stigma is entirely appropriate. By accidentally straying from the party line, Trump has highlighted some inconvenient implications of that view.