To see what immigration hard-liners really have in mind, ride the Lake Shore Limited between Chicago and New York or Boston. It is a daily Amtrak train that is regularly boarded and searched by the Border Patrol, even though it does not cross any international border.

As Nina Bernstein of The Times reported on Monday, border checkpoints aren’t just at the border anymore. She rode the train in western New York and found agents roaming the aisles, questioning passengers about their citizenship and removing those who could not prove they were here legally. What she described looked like just the kind of aggressive internal immigration enforcement that right-wing politicians have clamored for, but is arbitrary, oppressive and dangerously prone to racial profiling.

The Border Patrol says agents ask for people’s documents as part of a “consensual and nonintrusive conversation.” Passengers could decline to answer, but some told Ms. Bernstein that was theoretical, if not fictional, especially on a darkened train at 2 a.m. And train riders and civil-rights advocates told Ms. Bernstein that the burden of document checks falls hardest on people who look like foreigners. A woman who encountered the Border Patrol while riding a train with her boyfriend, who is Mexican, said: “You’re sitting on the train asleep, and if you don’t look like a U.S. citizen, it’s ‘Wake up!’ ”

This should not be happening. We are well aware of the federal crackdown on illegal immigration, sparked by the clamor for fencing and troops at the border. But we do not recall any discussion of imposing internal immigration checks on public transportation, with agents with dogs and guns randomly hauling people off trains.