On Tuesday, Panama launched a big new program to deal with illegal immigrants passing through the country. Here’s the twist: US taxpayers will be picking up the tab to send these migrants back to their home countries. This move is part of a new plan by Panama’s President Jose Raul Mulino to stop his country from being a major route for people trying to get to the United States.

Last year, over half a million migrants crossed the dangerous Darien Gap, a jungle area between Panama and Colo...