But when he tweets that immigrants coming across the border should have no due process rights – as he did this weekend – it’s time to stand up and take notice.

Due process of law is a fundamental bulwark against tyranny. It traces its origins back 800 years to King John and the English Magna Carta. In our Constitution, the principle was first enshrined in the Fifth Amendment and provides that “No person shall … be deprived of life, liberty, or property, without due process of law.” The same principle was later repeated in the Fourteenth Amendment.

As the language of the amendments makes clear and as the Supreme Court has recognized many times, “No person” means citizen and noncitizen alike. “[O]nce an alien enters the country, the legal circumstance changes, for the Due Process Clause applies to all ‘persons’ within the United States, whether their presence is lawful, unlawful, temporary, or permanent.” Zadvydas v. David, 533 U.S. 678, 693 (2001).

So, when the president of the United States starts talking about taking due process rights away from anyone, we shouldn’t shrug it off as just rhetoric meant to energize his base. Instead, we should be alarmed – not simply by the president’s profound ignorance but by what he might try to do next.

I always recoil whenever someone starts suggesting that we’re on a slippery slope heading to something akin to the Holocaust. But, I must admit that when I read about the president’s anti-immigrant tweet, I thought about the famous words of German theologian Martin Niemoller:

First they came for the Socialists, and I did not speak out—

Because I was not a Socialist. Then they came for the Trade Unionists, and I did not speak out—

Because I was not a Trade Unionist. Then they came for the Jews, and I did not speak out—

Because I was not a Jew. Then they came for me—and there was no one left to speak for me.

The lesson, of course, is clear. We can never shrug off threats to liberty. We must always speak out. We must always resist.

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The Southern Poverty Law Center is operating the largest pro bono deportation defense initiative in the country, with satellite locations at five immigrant detention centers in the Deep South and affiliates at six other locations. Click here for more information about the Southeast Immigrant Freedom Initiative.