Opinion writer

New U.S. citizens wave flags during a special Flag Day naturalization ceremony at the New York Historical Society, Tuesday, June 14, 2016, in New York.(AP Photo/Bebeto Matthews)

There is no issue more central to Donald Trump’s campaign. He spent a large chunk of the Republican convention and his acceptance speech haranguing viewers about illegal immigration, murders by illegal immigrants, jobs taken by illegal immigrants, etc.

It is worth returning to the issue as frequently as necessary to debunk his misrepresentations. The core of Trump’s campaign is built on fear about illegal immigrants, whom he would like to blame for much of our economic stagnation. If that is a web of lies, there is not much else to his campaign.

We know that two assertions Trump makes are false: that we are being inundated with illegal border crossings, and these people contribute significantly to unemployment.

On the number of illegal immigrants coming from our southern border, Trump seems just to make up numbers. Glenn Kessler explains:

Legal immigration flow has increased in the past four decades, and has remained at roughly 1 million people obtaining lawful permanent resident status every year since 2001. The unauthorized immigrant population increased from about 4 million in 1990 to about 12 million in 2007. But researchers estimate net zero illegal immigration flow from 2007 to 2014, due to the number of unauthorized immigrants leaving the country after the economic recession. Preliminary research from 2015 suggests net illegal immigration may have increased.

The “flood” simply is not there.

Even more important, Trump badly distorts the relative size of our immigrant population. We have not had “decades of record high immigration,” as he said. David Bier says that immigration peaked in 1991 at 1.8 million. He continues:

Rather than “decades of record immigration,” out of the top ten highest levels of all time, five occurred since 1990 and five before 1915.

But measuring immigration in terms of the absolute number of permanent residents is narrow and misleading. The biggest problem is that it implies that a million immigrants entering China, with a population of 1.4 billion, would have the same effect on employment as a million entering Estonia with a population of 1.2 million. Clearly, to understand the impact of immigration, you need to control for the size of the destination country.

By that measure, Bier reports that we have had “decades of below average immigration. Indeed, per capita immigration during the current decade is almost 30 percent lower than the historical average, and five times less than the record rates in the 19th and 20th centuries.” (Emphasis added.) Oops. Yeah, Trump is telling us quite a whopper in order to make illegal immigrants the bogeymen and justify his monstrously expensive wall and illegal roundup of 11 million people.

The connection between immigration and unemployment, we have argued, is phony, a product of the “lump of labor fallacy” (i.e. there are only so many jobs). But there is more: Immigration actually coincides with times of higher employment. Bier explains:

Unemployment is highest when immigration is lowest. During years when immigration was above the historical average, unemployment was 5.7 percent. During all other years, it was 7.2 percent, a difference of 1.5 percent. If you exclude years where unemployment dropped solely because of the draft, during the World Wars, the difference rises to 1.8 percent. . . .

When unemployment is high in the top H-1B fields, employers submit dramatically fewer applications. Companies hire foreign workers when they are making general increases in employment, not when they are laying off workers.

To be clear, immigrants are not causing the unemployment rate to move up or down. The economic literature on this point is quite unambiguous: immigrants cause essentially no effect on the unemployment rate one way or another. Rather, the causation is the other direction. Immigrants come during periods of economic growth when companies are hiring new workers, both immigrants and natives.

Indeed the recession and limp economy in the United States since 2008 explain why net migration is tapering off. Immigrants don’t go to an economy in downturn. They go where the jobs are.

It is hard to convince those so invested in anti-immigrant rhetoric that they are wrong. It’s easy to blame “others” rather than complicated forces such as automation and globalization for unemployment. It’s certainly harder to examine one’s own life choices (e.g. failure to graduate from college) in an economy in which circumstances have changed dramatically (e.g. high-paying, low-skilled jobs are going away). That is no excuse, however, for politicians to lie and whip up bigotry. And there’s even less justification for a flock of GOP politicians and pundits to go along with it.