WILLIAM BRANGHAM: Earlier this month, federal prosecutors moved to strip citizenship from 25 naturalized Americans, accusing them of lying about their pasts and hiding serious crimes.

It's called denaturalization, and the Justice Department now calls it one of its top priorities.

Justice correspondent Ali Rogin looks at what's behind this dramatic shift in law enforcement strategy.

ALI ROGIN: Since President Trump returned to office, the Justice Department has filed more denaturalization complaints than the Biden administration did during its entire four years.

To help us understand why they're using this tool more, I'm joined by Cassandra Burke Robertson, a law professor at Case Western Reserve University.

Cassandra, thank you so much for being here.

I first want to ask you, how does the Trump administration's use of this tool differ from what we have seen from previous administrations over the past few decades?

CASSANDRA BURKE ROBERTSON, Professor of Law, Case Western Reserve University: Yes, I think that the Trump administration's use of denaturalization differs in a couple big ways.

One of those is that the Trump administration is just filing many, many more cases.

Another way that they are differing from previous administrations is that these statements put out by the Trump administration seem to suggest that denaturalization is an end goal all by itself and that it's in fact part of the administration's immigration priorities.

And then the third way that the administration has used it differently is that the administration has used denaturalization as a political tool.

So the administration has talked very specifically about pursuing denaturalization against individuals that have made statements that perhaps angered the government.

ALI ROGIN: And you mentioned how this administration is using denaturalization as an end goal in and of itself.

How does that differ from what used to be done?

What sort of cases might be subject to denaturalization?

CASSANDRA BURKE ROBERTSON: So, in the modern era, denaturalization has been incredibly rare, less than 10 cases a year, on average.

And, generally, the cases that we have seen have been cases involving issues of national security.

So, for example, we saw denaturalization cases against former Nazi concentration camp guards.

And we saw a few denaturalization cases brought as part of the war on terror, trying to focus in on national security interests.

ALI ROGIN: And, in your review of these cases, do any of them strike you as ones prior administrations would have also sought denaturalization for?

CASSANDRA BURKE ROBERTSON: there are a few that likely would have been brought under any administration.

But the current administration is filing some cases based on facts that happened years ago or decades ago, when other administrations could have reviewed those same facts and decided to file a denaturalization case, but didn't decide to do so.

ALI ROGIN: Could this be further politicized or weaponized?

I'm thinking here of New York City Mayor Zohran Mamdani, himself a naturalized citizen.

Some of his critics, including a couple of Republican lawmakers, have called for his citizenship to be revoked and for him to be deported.

Is he a possible target here?

CASSANDRA BURKE ROBERTSON: It's not a realistic proposition, in the sense that if they were to try to denaturalize somebody like Zohran Mamdani, he has access to the absolute best attorneys.

The constitutional issues would be fully litigated.

I think he would lodge a very quick and strong defense.

ALI ROGIN: The Trump administration in most of these cases cites as part of the basis for bringing these complaints lying about somebody's past in order to gain citizenship.

Is that in and of itself enough to qualify for denaturalization?

CASSANDRA BURKE ROBERTSON: It is not enough by itself.

The Supreme Court has said that, if somebody makes a misstatement as part of the naturalization process, the government has to show materiality, that the misstatement would have made a difference, that somebody -- in the most common situation, the person would not have been granted citizenship if the government had been told the truth.

ALI ROGIN: Who adjudicates these cases?

Where -- how do they move through the system?

CASSANDRA BURKE ROBERTSON: They go to federal court.

And, in court, the government has to prove that the elements of the denaturalization case are satisfied, so typically showing that somebody maybe lied materially in the process.

So, once somebody loses citizenship status, whatever facts were brought as part of that denaturalization proceeding can also then be used in a subsequent removal proceeding or a deportation proceeding.

ALI ROGIN: Cassandra Burke Robertson with Case Western Reserve University, thank you so much for joining us.

CASSANDRA BURKE ROBERTSON: Thank you.