Donald Trump is a walking illustration (a cartoon, really) of why immigration is a Catch-22 for Republicans. Harsh rhetoric on the issue has vaulted the real estate mogul to the front of the GOP presidential pack. At the same time, his incredibly tone-deaf comments warning of Mexican "rapists" are keeping Republican consultants worried about the Latino vote awake at night.

Trump has lost a lot of business partners because of what he said about illegal immigration from Mexico. But he's gained among Republican primary voters who don't trust their leaders on immigration, and are tired of debating the issue in politically correct clichés.

The Donald is polling as high as second in both Iowa and New Hampshire. He leads in a Public Policy Polling survey of North Carolina Republican primary voters. He has taken his first lead in a national poll.

How did this happen? How can a candidate who has previously supported single-payer health care, gun control, legal abortion, and tax increases suddenly capture the imaginations of the most passionate Tea Party conservatives? Trump is a former Hillary Clinton donor, for goodness sake!

Well, here's how it happened: Trump is combative where the Republican establishment is deemed pusillanimous. Sometimes that trumps ideology and policy. He is giving voice to concerns grassroots conservatives have that respectable Republicans are unwilling or unable to articulate.

More than four-fifths of Republican voters told Gallup they are dissatisfied with the current level of immigration. That's up 19 percentage points in a year. A large majority of these dissatisfied Republicans want less immigration, not more.

Who speaks for this position? Even most of the anti-amnesty candidates who are running consider our existing legal immigration numbers sacrosanct. Rick Santorum has called for cutting immigration, but despite his best efforts, he is still primarily identified with traditional social issues like abortion and gay marriage.

Nearly every Republican running for president has expressed support for a path to citizenship or legal status for most illegal immigrants already in the United States, either in the past or as something they might be open to in the future. This even includes Trump, though his bombastic rhetoric far outweighs any nuance that might creep into his position.

That's a good thing for Trump, because the Republicans most angry about mass immigration have come to see nuance as a sign they are about to be sold out. You can get majorities, even large majorities, to say they support legalization of illegal immigrants if certain enforcement and security conditions are met. But they don't really believe the enforcement will happen, just like it didn't after the 1986 amnesty.

Such conservatives have watched Republicans run for office saying an "earned path to citizenship is basically code for amnesty" and then join the Gang of Eight once elected. They've seen John McCain team up with Ted Kennedy on immigration and then grudgingly tell Vanity Fair he will "build the goddamned fence" if conservatives want it. Facing a primary fight for his Senate seat three years later, he revised this to "Complete the dang fence," as if it was originally his idea.

The trouble with the Republican war on nuance is that the sophisticated case against continuous mass immigration is nuanced. It turns on numbers, and time, and skill levels relative to the U.S. labor force.

That case seldom gets a hearing because it is caricatured as viewing immigrants themselves as a kind of contaminant, the basest form of racial politics. What do immigration hawks like Trump do? Reinforce the caricature.

When immigration is only discussed the way Archie Bunker used to argue with Meathead in All in the Family, important things are left out. This includes the economic prospects of Americans without high school diplomas, themselves disproportionately black and Latino. The challenge of admitting so many immigrants on family-reunification grounds, in some cases to do jobs that mechanization may eliminate in our lifetimes. The immigration component of economic and social problems ranging from poverty to the number of people without health insurance.

Lower immigration levels are worth pursuing as a way of reducing the salience of racial and ethnic politics, turning down the temperature in our public fights over affirmative action and bilingual education. The economic benefits of our current immigration policies are not universally shared, even if it leads to an uptick in GDP.

Factor this into the argument that relatively lower-skilled immigrants should be imported to work at above-average labor force participation rates to sustain aging white natives by paying into Social Security and Medicare. You don't have to be a racial demagogue to conclude this isn't a recipe for social harmony. It is actually a recipe for the success of racial demagogues.

Are there any responsible people who want to address the issues Donald Trump is riding to the top of the Republican field?