Now many liberal Democrats, including those who call for the abolition of Immigration and Customs Enforcement, seek to erase the distinction between legal and illegal immigration. Under the banner of inclusiveness, equality, human rights, racial reconciliation and reparations for American interventions in the third world, those liberals demand sanctuary for those who make it past the Border Patrol or overstay a visa. Few speak openly of open borders, but that is essentially what they are calling for.

Over the years, righteous outrage against restrictionists has been fueled by some truly odious people. Lance Morrow of Time magazine described the problem in 1980: “Ku Klux Klansmen have paraded around Florida lately, dispensing their old nativist bile and giving a bad name to an argument (‘America for Americans,’ the picket signs say) that has more thoughtful and respectable proponents.”

Today, President Trump has brought such outrage into the mainstream with the repugnant charge that unauthorized immigrants “infest our country.” But Mr. Trump does not deserve all the blame for our dysfunction. The immigration debate has been warped by tribal passions on the left as well.

What the left misses is that as Mr. Trump pursues his draconian efforts to stem the tide, many Americans think he is fighting the good fight. They may be dismayed at his manic nastiness and his proclivity for crude insult. But they admire his willingness to wage what they see as a patriotic battle to defend common people.

Arthur Schlesinger Jr., the prominent liberal historian, believed that immigration restrictions were essential. He wrote in “The Disuniting of America” that while “any curtailment of immigration offends something in the American soul,” it was also true that “uncontrolled immigration is an impossibility.”

President Ronald Reagan in 1986 proclaimed that he and Congress had fulfilled that duty. He signed the Immigration Reform and Control Act, combining an amnesty with a program to stop future illegal immigration by requiring employers to verify that their new hires were legal.

The amnesty was delivered. Work-site enforcement was not. Illegal immigration exploded. From 1990 to 2007, the unauthorized population grew at an annual average of 500,000. It reached a peak of 12.2 million in 2007, before falling to its present level of about 11 million.