Throughout Tuesday’s oral arguments in Gill v. Whitford, Justice Anthony Kennedy and the Supreme Court’s left-leaning justices grilled Wisconsin’s attorneys with tough questions that suggest a majority of the court is prepared to impose constitutional limits on political redistricting. The highlight of the hour came when Justice Sonia Sotomayor posed a very simple inquiry that cut to the core of the case: “Could you tell me what the value is to democracy from political gerrymandering? How does that help our system of government?”

Sotomayor’s question arrived after the justices had debated abstract principles of law (and math) for nearly half an hour. Kennedy and the liberals had already laid out their constitutional case against partisan gerrymandering: When Republicans draw district lines designed to dilute the power of Democratic votes, they are punishing Democratic voters for associating with, and expressing support for, the Democratic Party. (The same goes, naturally, for Democrats drawing district lines to dilute the power of Republican votes.) This viewpoint-based burden on the right to vote clearly infringes upon the freedom of expression and association protected by the First Amendment. Given that the First Amendment is the cornerstone of self-governance, political redistricting would seem to pose a grievous threat to representative democracy, entrenching undemocratic legislative majorities by penalizing voters who openly support the minority party.

It can be easy to get lost in the technicalities of constitutional doctrine, or the putative gobbledygook of gerrymandering math, and lose sight of the broader principle at stake. Sotomayor, though, has never been one to lose sight of first principles. Her question on Tuesday was simple but devastatingly effective. Erin E. Murphy, the attorney representing Wisconsin’s (very gerrymandered) State Senate, had no good answer for Sotomayor. “I don’t think that … districting for partisan advantage has no positive values,” Murphy began hesitantly. She continued:

I would point you to, for instance, Justice Breyer’s dissenting opinion in [2004’s Vieth v. Jubelirer] which has an extensive discussion of how it can actually do good things for our system to have districts drawn in a way that makes it easier for voters to understand who … the legislature is. It produces values in terms of accountability that are valuable so that the people understand who isn’t and who is in power.

“I really don’t understand what that means,” Sotomayor responded.

Neither do I, since Breyer’s Vieth dissent says pretty much the opposite of what Murphy claims. (When “the minority’s hold on power is purely the result of partisan manipulation,” Breyer wrote, the legislature has engaged in “a serious, and remediable, abuse, namely … unjustified entrenchment.”) As legal analyst Mike Sacks noted on Twitter, Murphy is an excellent attorney; if “such a simple question renders her into word salad, there’s a problem.”

Sotomayor then drilled down and posed an even sharper follow-up question to Murphy: “It’s OK to stack the decks so that for 10 years—or an indefinite period of time—one party, even though it gets a minority of votes, can get … the majority of seats?”* Murphy’s response:

With all due respect, you know, I would certainly dispute the premise that the decks are stacked here. At the end of the day, what matters is how people vote in elections and that’s what’s going to determine the outcomes, as it has in Wisconsin where the Republicans have won majorities because they’ve actually won the majority of the vote in most of the elections over the past four years.

While the words in this paragraph did have the benefit of cohering into intelligible English sentences, Murphy’s answer again made no sense. In 2014, Wisconsin Republicans received 52 percent of the vote and won 63 out of 99 seats in the State Assembly. In 2016, they won the same percentage of the statewide vote and captured 64 seats. Murphy’s rosy response was technically correct, but it elides the fact that Republicans won a bare majority of votes overall yet captured a near-supermajority of assembly seats. Moreover, she conveniently ignored the 2012 election from her response. Perhaps that’s because in 2012, Wisconsin Republicans won just 48.6 percent of the statewide vote—and captured 60 out of 99 seats. That’s what a stacked deck looks like.

This is far from the first time that Sotomayor has put a resourceful advocate in a very tight spot. The justice performed a similar trick at her very first Supreme Court oral arguments in Citizens United, when she interrogated Floyd Abrams about the dubious wisdom of corporate personhood. Many conservatives spurn Sotomayor as a minor intellect, sometimes out of racism, but frequently due to a misunderstanding of her jurisprudential style. When questioning counsel, Sotomayor would rather zero in on factual flaws and spurious assumptions than spin out twisty doctrinal hypotheticals. While critics mistake this for a lack of sophistication, in actuality it shows her hunger to strike at the heart of the issue before the court with minimal pretension or delay.

Sotomayor’s barbed colloquy with Murphy laid bare the fundamental weakness in Wisconsin’s defense. The state cannot honestly justify its own gerrymandering; it can only insist that court intervention would somehow make the problem worse. As Gill demonstrates, Sotomayor might not always ask the most elaborate questions, just the most important ones.

*Correction, Oct. 5, 2017: This article originally misquoted Supreme Court Justice Sonia Sotomayor. She said that, in a politically gerrymandered state, the minority party can get a majority of seats in the legislature, not that they can’t. (Return.)