THE LAST ONES IN ALWAYS HATE THE NEXT ONES IN:

Trump would abolish birthright citizenship: the principle, embedded in the 14th Amendment to the Constitution, that anyone born in the United States is an American, no matter the legal status of his or her parents. Sen. Ted Cruz promptly claimed he'd always opposed birthright citizenship, too, a claim the Houston Chronicle quickly disproved. Bobby Jindal and Ben Carson joined in, as did Scott Walker, though he didn't seem entirely sure. Jeb Bush stayed admirably aloof from the mob.

Other conservatives pushed back, but often half-heartedly, arguing that the law would be too hard to change, or that it shouldn't be the focus of anti-immigration sentiment because it isn't the biggest problem.

But that's wrong, too. Birthright citizenship isn't a problem at all. It's one of the things that makes America great.

For many countries, what is in your blood, or your DNA, defines whether you can belong. I was shocked that people who had been born in Japan, and in some cases whose parents had been born in Japan, were not Japanese citizens, though they knew no other country. The fact that their ancestors had come (or been brought) from Korea disqualified them from automatic citizenship at birth.

Americans, by contrast, are bound together by a civic ideal.

"Birthright citizenship is much more about us, a nation formed and held together by civic values, than it is about immigrants themselves and an incentive or disincentive to come here legally or illegally," says Doris Meissner, who ran the U.S. immigration agency under President Clinton and is now a senior fellow at the Migration Policy Institute.

"What's the belief system, the social cohesion that binds us?" she continues. "A commitment to democracy, participation, equal rights, opportunity, due process, government by the people -- people have to be full members of the society for that to be real and flourish."

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