Pete Buttigieg suddenly seems presidential. The mayor of South Bend, Indiana, has surged in the polls, zipping ahead to third place in Iowa and New Hampshire. He’s hauling in cash—more than $7 million in the first quarter of 2019—and raised another million hours after he formally announced his candidacy for president on Sunday. Buttigieg has been profiled by national outlets over and over and over again, so we know a great deal about his personal life (veteran, polyglot, Rhodes scholar), his husband (a social media star), and even his dogs (Buddy and Truman, rescues, also social media stars). What we do not know much about is how, exactly, Buttigieg would govern the nation if elected. Beyond endorsing a few standard Democratic goals—LGBTQ equality, voting rights, and gun control chief among them—Buttigieg has been hazy on policy. His beautifully designed technicolor website has no policy section, nor do most of his speeches. Right now, he seems to be running on “vision” and charisma.

The one concrete policy Buttigieg has proposed that separates him from the Democratic pack: court reform. While he’s open to simply adding seats to the Supreme Court, Buttigieg has said he’d prefer an appellate rotation plan. This scheme would expand the court to 15 seats—five filled by Democratic appointee, five by Republican appointees, and five selected from lower courts by the other 10 justices. It sounds sensible, balanced, and durable, and it may be all of those things. Unfortunately for Buttigieg, it is also clearly unconstitutional.

How did Buttigieg get to a point where his most distinctive policy position is unworkable? First, court packing has become a hot-button issue in the 2020 Democratic primary. That makes sense, as the Supreme Court’s sharp turn to the right was facilitated by Republicans’ blockade of Merrick Garland and eventual abolition of the judicial filibuster to confirm Neil Gorsuch, followed by the controversial confirmation of Brett Kavanaugh. Sens. Kamala Harris, Elizabeth Warren, and Kirsten Gillibrand have refused to rule out adding seats to the court, as has former Rep. Beto O’Rourke. Most candidates are vague about the details: Harris, for instance, has said that “everything is on the table,” while Gillibrand has described the addition of justices to the bench as one of several “interesting ideas that I would have to think more about.” Like Buttigieg, O’Rourke has expressed curiosity about the appellate rotation plan, calling it “an idea we should explore.”

The entire purpose of liberal court reform is to make the court more liberal.

This hand-waving implies that two proposals, court packing and appellate rotation, are both “on the table” and, perhaps, equally viable and desirable. That’s a problem, because one proposal (court packing) is perfectly legal, while the other (appellate rotation) is plainly unconstitutional.

Start with basic court packing—the addition of more justices (typically between two and six) to the Supreme Court. Nothing in the Constitution prohibits this maneuver, since the Constitution does not prescribe the number of seats on the court. Various federal laws have set this number as low as five and as high as 10. It is currently fixed at nine, but Congress can change that through legislation. If it did, then the president could nominate the new justices and they would join the bench upon Senate confirmation, casting full and equal votes.

Appellate rotation is a substantially heavier lift. Also called the 5-5-5 plan or the “balanced court solution,” the 10 partisan justices would pick the remaining five justices from the federal courts of appeals and would need to select them unanimously. If the 10 partisans could not agree, they would lack a quorum to hear any cases. The Supreme Court’s work would grind to a halt until they reached a compromise.

This plan’s appeal is obvious—it gives neither party an advantage and thus avoids the judicial arms race that could result from straightforward court packing. Its flaw, however, is fatal. As Pack the Courts has explained in a white paper, the Constitution’s Appointments Clause declares that the president “shall appoint” Supreme Court justices “with the Advice and Consent of the Senate.” The justices themselves have no power to appoint other justices; that authority is explicitly assigned to the president alone. If Congress forced the president to share appointment power with the justices, it would radically alter a key constitutional procedure. That cannot be done by mere legislation. It requires nothing less than a constitutional amendment.

When Buttigieg (and O’Rourke) float appellate rotation as an alternative to court packing, they presumably intend to come across as moderate, even nonpartisan. Court packing has the evident goal of neutralizing conservative dominance on the Supreme Court by tilting the bench to the left. Appellate rotation, by contrast, sounds technocratic and centrist. Buttigieg insists that he does not want to “make the court more progressive” but rather wishes to “arrest the decline in the perception of the court toward being viewed as a nakedly political institution.” Appellate rotation “takes the politics out of it a little bit,” making it the “most intriguing” option to him. “If we want to save that institution,” Buttigieg asserts, “I think we better be ready to tune it up as well.”

That line might poll well, but it’s the wrong way of looking at court reform—and not just because the “most intriguing” option is also unconstitutional. Buttigieg may not want to cross the Rubicon of altering the makeup of the Supreme Court, but Republicans already blew past that norm. In 2016, Republicans proposed, and partially enacted, their own version of court reform by refusing to even hold hearings for Garland. The GOP effectively shrank the size of the court to eight seats for more than a year, resulting in deadlocks that hobbled the court’s work. Then, multiple Republican senators—including John McCain, Ted Cruz, and Richard Burr—announced that they would not confirm any nominee put forward by Hillary Clinton if she won the presidency. Burr said he would “do everything I can do to make sure four years from now, we still got an opening on the Supreme Court.” Sympathetic commentators like Ilya Shapiro cheered them on, arguing that it would be “honorable” for the Senate to refuse to confirm Clinton’s nominees and “let the Supreme Court die out, literally.”

The entire purpose of liberal court reform is to make the court more liberal, just as the point of Republicans’ 2016 blockade was to make the court more conservative. Buttigieg should not hide the ball and pretend to have some higher, impartial goal. Instead, he should heed the lesson of Democrats’ 1937 debacle, when President Franklin Delano Roosevelt lied about the objective of his court-packing bill. Roosevelt claimed that he wanted to expand the Supreme Court not because it kept striking down New Deal legislation but because the justices were too old to do their jobs efficiently. This contention was easily disproved by the fact that the court’s oldest member, Justice Louis Brandeis, generally voted to uphold the New Deal. And it stymied honest debate about the court’s proper role in American democracy, leading to a crushing legislative defeat of Roosevelt’s bill, aided by senators who would not feign belief in the president’s pretenses.

If progressives are worried about the direction of the Supreme Court—if they think its majority is motivated by a partisan desire to crush Democrats, harm workers, and kneecap democracy—they should be candid about their plan to fight back. They should not conceal the aims of liberal court reform or allege that an unconstitutional plan like appellate rotation is actually a viable solution. If Buttigieg is truly alarmed by today’s Supreme Court, he should acknowledge that it doesn’t need a wonky “tuneup.” It needs more liberal justices.