The right way to deal with the caravan crisis is to make clear that it is no crisis. The marchers pose no threat. The United States has clear laws governing refugees and well-funded agencies to enforce those laws, and it’s an embarrassing waste of money to send troops to the border. In fact, illegal border crossings have significantly declined in recent years. The country must and will continue to enforce the laws that control its borders, as Mr. Obama himself did as president during an earlier, actual surge of Central American migrants, when he took the difficult step of dispatching National Guard troops to the border and detaining many mothers and children.

Longer-term questions about how to put the country’s approach to immigration back on a rational, moral foundation are more difficult. Republican hard-liners defeated bipartisan attempts at comprehensive immigration reform in 2007 and 2014. In the Trump era, Democrats have found the issue of immigration even more confusing; a couple of Democratic senatorial candidates have even lined up behind Mr. Trump.

Mr. Trump’s cruel treatment of immigrants and race-baiting about nonexistent threats do not amount to a solution. Managing the entry of refugees and other immigrants, and creating a fair system to deal with the millions of undocumented immigrants within the borders, are serious matters in need of common sense and elemental humanity.

The country needs to streamline the asylum system and establish generous quotas of immigrants and refugees from around the world. To be effective, any immigration plan has to include serious development aid to Central America’s troubled states. Cutting off what little aid they get, as Mr. Trump has threatened to do, will only create more caravans.

People seeking to partake of the American dream have always been central to America’s identity and strength. How the country treats them goes straight to its core values. The Democrats cannot sit this one out, especially when the Republican leader is so blind to the true sources of America’s greatness.

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