Chief Justice John Roberts has claimed that he is “the most aggressive defender of the First Amendment on the court now.” He has the opportunity to make good on his claim when the Supreme Court hears two big partisan gerrymandering cases today.

This Term’s blockbuster gerrymandering cases—Rucho v. Common Cause and Lamone v. Benisek­, both up for argument this morning—shine a light on some of the most extreme efforts by state legislatures to use their power to draw district lines to rig the electoral process and disadvantage voters with whom they disagree.

Rucho involves North Carolina’s 2016 congressional districting plan, which was drawn explicitly to ensure Republican candidates won ten out of thirteen seats by “packing and cracking” Democratic districts whenever possible. Republicans in control of the state legislature were up front about their efforts to maximize their hold on power. Representative David Lewis said that “electing Republicans is better than electing Democrats. So I drew this map to help foster what I think is better for the country.”

Republican mapmakers would have gone even further but, as Lewis explained, “I do not believe it’s possible to draw a map with 11 Republicans and 2 Democrats.” The 2018 elections offer proof of just how enduring this gerrymander was: even in a wave election, Democrats could only eke out the same three seats. Gerrymandered districts, as one report stressed, proved to be stronger than a blue wave.

The facts of Lamone are similar, except in that case it was a Democratic state legislature, not a Republican one, seeking to entrench the party in power. In 2011, the Maryland legislature redrew the 6th Congressional District to flip the district from Republican to Democratic, ensuring all but one of Maryland’s congressional seats would be held by Democratic candidates. To achieve this end, the mapmakers shuffled hundreds of thousands of citizens out of or into the 6th District, using sophisticated political data to dilute the votes of Republican voters.

The reason why state partisan gerrymanders offend the First Amendment is pretty basic, drawing on deeply rooted First Amendment principles that have been reaffirmed by the Supreme Court time and again. First, the First Amendment protects the right of individuals to associate with the political party of their choice. This reflects that the First Amendment helps to safeguard our democracy. Second, efforts by the government to subordinate persons on account of their political affiliation—such as by diluting their votes—violate the First Amendment’s core guarantee. That’s viewpoint discrimination pure and simple.

The First Amendment simply does not let the government tamper with our democracy in this way. As James Madison observed, the First Amendment ensures that “those in power” may not “derive an undue advantage for continuing themselves in it; which, by impairing the right of election, endangers the blessings of the government founded on it.”

Chief Justice Roberts does not need to rely on James Madison’s words to strike down extreme partisan gerrymanders as a violation of the First Amendment; he can simply recite his own. Chief Justice Roberts’ campaign finance jurisprudence offers a roadmap for striking down the North Carolina and Maryland partisan gerrymanders as a violation of the First Amendment.

Take the Chief Justice’s 2011 opinion in McCutcheon v. FEC, which opened with the recognition that there is “no right more basic in our democracy than the right to participate in electing our political leaders.” In that ruling, which struck down federal aggregate contribution limits, Roberts stressed that the First Amendment prevents the government from “compromising the political responsiveness at the heart of the democratic process, or allowing the Government to favor some participants in that process over others.” That fits partisan gerrymandering to a T.

In his campaign finance rulings, Chief Justice Roberts has repeatedly made the point that the First Amendment does not permit the government to entrench itself in power, such as by enacting regulations that make it harder for challengers to raise and spend money. As Chief Justice Roberts wrote in McCutcheon, in our constitutional system, “those who govern should be the last people to help decide who should govern.” He made a similar point in an earlier campaign finance case, Arizona Free Enterprise Club’s Freedom Club PAC v. Bennett, writing that the “basic intrusion by the government into the debate over who should govern goes to the heart of First Amendment values.” This statement encapsulates why partisan gerrymanders violate the Constitution: voters should choose their representatives, not the other way around.

Despite all this, most observers expect that Chief Justice Roberts will vote to uphold the partisan gerrymanders in these cases. Indeed, during oral argument in Gill v. Whitford, a partisan gerrymandering case the Court heard last year, Chief Justice Roberts expressed concern about “taking these issues away from democracy and . . . throwing them into the courts” based on what he termed “sociological gobbledygook.” Roberts insisted that the Court’s ruling had to be based on “language in the Constitution.” Otherwise, Roberts said, “the intelligent man on the street is going to say that’s a bunch of baloney. . . . And that is going to cause very serious harm to the status and integrity of the decisions of this Court in the eyes of the country.”

Chief Justice Roberts was too dismissive of social science evidence, which can often play an important role in constitutional litigation. But he was right that the Justices ought to root their rulings directly in the Constitution. And he can do that in the partisan gerrymandering cases. To strike down these partisan gerrymanders, he only needs to enforce the First Amendment’s guarantee, which protects the right to associate with the political party of one’s choice and forbids the government from subordinating voters because of the political party to which they belong. As the Chief Justice’s rulings underscore, the First Amendment denies the government the authority to entrench one party in power. A state cannot enact into law the view that “electing Republicans is better than electing Democrats,” or that electing Democrats is better than electing Republicans. Those decisions must be made by the people, not the government.

Chief Justice Roberts has positioned himself as the Court’s most insistent defender of First Amendment freedoms. The Court’s upcoming partisan gerrymandering cases will test whether Roberts deserves that accolade.