Donald Trump believes the best way to prevent the mass shooting in Orlando is to go back in time and block shooter Omar Mateen’s parents from coming to the United States.

"The bottom line," Trump said in a major speech on Monday, "is that the only reason the killer was in America in the first place was because we allowed his family to come here."

This was all, Trump continued, that could have been expected — once Muslim immigrants are admitted into the US, their descendants will inevitably become terrorists. Under President Hillary Clinton, he said, "you'd be admitting hundreds of thousands of refugees from the Middle East with no system to vet them, or to prevent the radicalization of their children."

"Or their children’s children," he added, in an apparent ad lib.

Trump has called repeatedly to ban Muslim immigration to the United States. As his policy speech Monday in response to the Orlando shooting made clear, he sees the ban as his cardinal foreign policy proposal.

But he’s not being honest about it. Donald Trump has shown, time and time again, that he doesn’t believe the descendants of immigrants — whether they come from the Muslim world or from Mexico — are necessarily Americans.

At best, he needs them to prove their loyalty. At worst, he sees non-European immigrant heritage and Americanness as a zero-sum identity game — someone with the former can never truly claim the other.

For more than 200 years, "American" has been about something more than blood and surname. By accusing second-generation Americans of being un-American, Donald Trump, the son of an immigrant mother, is engaging in a little second-generation un-Americanness himself.

Trump consistently treats some Americans as not fully American

An instructive counterpoint: Here is what Donald Trump said during an interview about a mass shooting at Umpqua Community College in October, conducted by Christopher Harper-Mercer, a US citizen whose parents weren’t immigrants (emphasis added):

People are going to slip through the cracks [...] oftentimes this happens and the neighborhood’s just, you know, we sort of saw that about him, it really looked like he could be a problem but it’s often hard to put someone in an institution for the rest of their lives based on the fact that he looks like he could be a problem.

The contrast couldn’t be clearer. Some people get the benefit of the doubt: The suspicions of their neighbors aren't enough to punish them for something they haven’t yet done (and may never do). Other people don’t. The fact of their heritage not only puts them under suspicion of radicalization but makes them such a threat to the American homeland that it's worth banning their parents from the US just to prevent them from being born here.

The difference between the two groups isn't whether they’re American. Both Omar Mateen and Christopher Harper-Mercer were American in the eyes of the law. But in the eyes of Donald Trump — who said Monday that he wanted to be the president of "all Americans," even as he harped on the dangers of second-generation Americans — Mateen simply doesn’t count as American because of who his parents were.

"He was born an Afghan of Afghan parents who immigrated to the United States," Trump said during his Monday speech (in another apparent ad lib).

We’ve seen this distinction before. Gonzalo Curiel is a federal judge. Before being appointed to the federal bench, he was a distinguished prosecutor. Curiel is a second-generation American. He was born in Indiana; his parents were born in Mexico.

Shortly before the Orlando attack, Donald Trump spent more than a week saying that Curiel couldn't be objective toward Trump in a class-action suit because Trump wanted to build a wall with Mexico — implying, in a not-even-veiled way, that Curiel would put Mexico's interests in front of America’s.

Trump and his supporters pointed to Curiel’s membership in a Latino lawyers association, calling it a "radical" Latino organization. So Curiel, too, in his way, was accused of being a member of the radicalized second generation.

Literally all of American history has been about immigrants becoming American

The equality of all citizens is the cornerstone of American law. It is certainly the cornerstone of American immigration policy.

Not all people in the US have the same rights. Legal immigrants, even permanent residents, don’t have the full rights of citizens — they can be deported for committing a crime (and thousands of them are). Once an immigrant is naturalized as a US citizen, that stops. Citizens who commit crimes are punished by the US legal system; they're not sent out of the country — no matter where they’re from.

Any child born on US soil to parents living in the US is a citizen upon birth. (Even the Republicans who have floated restrictions on birthright citizenship haven’t gone so far as to withhold birthright citizenship to the children of US citizens, even if the parents weren’t born here.)

This is fundamental to how Americans understand their country. Most Americans (certainly most white Americans) believe in the idea of their country as a "nation of immigrants": the place where generations of people came from other countries to build a better life for themselves and their families, where the heritages of the "old country" were quietly subsumed by a broader American identity. America is where you go to become an American; if you want to become an American, the doors are (in theory) open to you.

Because the debate over immigration to the US (prior to the presidential candidacy of Donald Trump) focused on unauthorized immigrants, it's often been characterized as a debate over the "rule of law." (As a matter of fact, one of the most common lines heard among opponents of legalizing unauthorized immigrants is, "My ancestors came here the right way" — an acknowledgment that someone can become American from immigrant stock.)

Trump has blown the cover off that, by impugning the Americanness of legal immigrants and American citizens just as much as he’s attacked unauthorized ones. He's shown that many Americans are anxious, more than anything, about the threat immigrants pose to their values.

These Americans suspect there are some cultures that cannot simply be subsumed into American culture — that are completely inimical to Americanness. Immigrants from these cultures can't be expected (or shouldn't be trusted) to choose American values over the values of their home countries. If allowed to take root in American communities, they will simply promote pockets of separatism — cultural "no-go zones." And if their home countries come into conflict with America, they — and their children, and their children’s children — will choose heritage over patriotism.

The fear of a fifth column is nothing new, either: For as long as Americans have held up the ideal of the integrated or assimilated immigrant, they’ve been afraid that some immigrants are simply occupying America without joining it. These fears gave us anti-Catholic discrimination and riots in the 19th century. In the early 20th century, it gave us surveillance of German-American communities — and forced 120,000 Japanese Americans, many of them US citizens, into concentration camps.

Radicalization is a problem. Isolation helps feed it.

Second-generation radicalization of Muslim immigrants is a problem, both in the US and in many European countries. A federal court in Minneapolis is currently hearing the case of three Somali-American teenagers accused of having become radicalized by ISIS. Many other young men (some of whom immigrated at a young age themselves, others of whom are second-generation Americans) have been brought up on similar charges.

The question of how to prevent second-generation Americans (or Belgians, or Brits) from becoming radicalized is a tough one. It’s something that many people — specifically, Muslim community leaders — in both the US and Europe are working on. There aren’t good answers yet. Nor are there easy answers for how people become radicalized.

The evidence is suggestive, however, that one of the factors that makes young people most vulnerable to recruitment by radicals is social isolation. In particular, when young people feel disconnected from both the culture of their heritage and the culture of their countries, they are more likely to find a home in a radical ideology instead. One 2013 study of Dutch Muslims found that "a feeling of being disconnected from society" was an "important determinant of a radical belief system."

It’s nowhere near as simple as "if Americans don’t embrace second-generation immigrants, they’ll get radicalized." These are just factors in a larger matrix. But discriminating against second-generation young people on the basis of their heritage is certainly correlated with social isolation and radicalization.

More broadly, when second-generation young people feel that their identity is a zero-sum game — that the heritage of their parents is in conflict with the heritage of the country in which they live — they’re more likely to turn to radicalism to resolve the conflict.

A 2013 study of Turkish (Muslim) and Russian immigrants in Germany found that the more religious the immigrants were (or, in the case of Russian immigrants, the more attuned to ethnic identity), the less likely they were to be sympathetic to radical action. But when immigrants felt they would have to give up their Turkish or Russian identities in order to become German, they were more likely to nurture radical sympathies.

Identity doesn’t have to be a zero-sum game. Just look at Judge Curiel — who’s spent the bulk of his career working for the American government while remaining active in a group that celebrates his Latino heritage. Most studies of immigrant integration suggest that the most successful children of immigrants are those who manage to retain connections to both the heritage of their parents and the culture of the country in which they live.

But to Donald Trump (and many of his supporters), Curiel’s "pride" in his Mexican heritage was a threat of greater loyalty. The only way an immigrant — or the child of an immigrant, etc. — can prove she is truly American is to reject the identity of her ancestry.

Short of that, second-generation Americans are all equally deserving of scrutiny — they’re all, to some extent, impostor Americans, whose enemy loyalties will eventually come to the fore.

When you regard Gonzalo Curiel and Omar Mateen with exactly the same degree of suspicion, you give second-generation immigrants very few reasons to aspire to be Gonzalo Curiel. You give second-generation immigrants just one more reason to suspect that maybe the Omar Mateens of the world have it right after all.

It’s a pinched, insecure, petty way of looking at America. It’s what you might get if you looked at America and saw only a reflection of Donald J. Trump.