President Obama seems on the verge of the most abject diplomatic capitulation in American history — to Iran, our bitterest enemy — and Republicans are arguing about Donald Trump? The prospect of a deal with Iran is dumbfounding and infuriating, as the U.S. held all the cards in the protracted negotiations and yet executed serial surrenders to the Iranians, rather like a courtier bowing his way backward from a monarch.

While the Obama administration is paving the way for a possible mushroom cloud over Tel Aviv or New York in the near term, we’re all tying ourselves in knots about what Trump said about Mexicans. The Democrats seem to have a Trump card.

Immigration arouses tremendous rage among both left and right. While I like a good brawl as much as the next person, it seems that Trump is the answer only if the question is: Why can’t we get more oafish egomaniacs into politics? Just when the Republican Party needs finesse and sensitivity when discussing immigration — just when it needs to focus on issues that unite all sectors of the electorate, including Hispanic and Asian voters — it gets a blowhard with all the nuance of a grenade.

Trump tarred most Mexican immigrants as drug-dealers, criminals and rapists, allowing only as an afterthought that some may be good people. He claimed to have discussed the matter with border guards. Would those officers please step forward?

Trump has achieved his objective — making himself the center of attention — but he has subtracted from our sum total of knowledge about the immigration issue. According to an analysis of Census Bureau data by the Immigration Policy Center, only 1.6 percent of immigrant males between the ages of 18-39 are incarcerated, compared with 3.3 percent of the native-born. But just as Dylann Roof doesn’t represent white people, Mexican rapists don’t represent anyone other than themselves.

Oddly, the entire brouhaha over immigration may be misplaced. The Census Bureau reports that starting in 2013, the country that sent the most immigrants to the U.S. was China, with 147,000, followed by India, with 129,000, and Mexico, with 125,000.

Some immigrants will doubtless continue to arrive. As Tamar Jacoby of ImmigrationWorks USA put it, “Once they see that you don’t have to bribe the police here, they’re satisfied.” There remains much to recommend the USA as a destination, and we’ve been lucky that our neighbors to the south roughly share our religion and civilization — unlike the Muslim immigrants who’ve flooded Europe during the same period.

But with world fertility rates declining, the U.S. may face an unexpected problem: too few immigrants. In 1960, half of the U.S. workforce consisted of high school dropouts. Today, it’s only 6 percent. Yet the jobs for low-skilled workers — busboys, chambermaids, food processing — remain. If employers cannot find workers for those jobs, there will be fewer managerial and executive positions for native-born Americans.

It’s a complex subject that deserves grownup discussion — exactly what Trump and his claque preclude.