Senate Democrats this afternoon secured the 41 votes necessary to filibuster the nomination of Neil Gorsuch to the Supreme Court. Critics of using the filibuster say that Democrats risk further eroding norms in the Senate and losing the chance of using the filibuster in the future, if Republicans make good on threats to trigger the so-called nuclear option and eliminate it.

But despite such hand-wringing, Democrats have a solid case for blocking the conservative favorite. It’s based on substance.

Senate Majority Leader Mitch McConnell (Ky.) has signaled that if Democrats filibuster Gorsuch, he will alter Senate procedures and eliminate the filibuster for future Supreme Court nominees. In changing the rules, Republicans will no doubt place the blame on Democrats, portraying them as the obstructionists.

But, putting aside the fact that Republicans didn’t even give Merrick Garland a hearing for months, Democrats are standing on the moral high ground on the merits. That’s because, at his confirmation hearings, Gorsuch steadily evaded questions designed to pin down his legal views, denying voters any insight into those views. This gives Dems both a defense against the “obstructionist” charge and gives them the better political argument.

Some have argued that Democrats should save their political capital for a future nominee. Gorsuch, this argument goes, won’t shift the balance of power on the court since his views essentially align with those of his predecessor, the late Antonin Scalia. Democrats, then, should hold their fire for a future Trump nominee to replace one of the liberal justices on the court, when the future of abortion rights, for example, hangs in the balance.

But Gorsuch has handed Democrats a robust case against his confirmation, and they should use it. First, there are his rulings. He ruled against a worker suing his employer in what’s now known as the frozen trucker case, siding with an employer who fired its driver Alphonse Maddin, for abandoning his incapacitated (and unheated) truck in subzero temperatures. Gorsuch also ruled for Hobby Lobby over its female employees, holding that a privately held corporation had a religious right to object to the contraception coverage requirement under the Affordable Care Act. In both, Gorsuch showed he’s inclined to interpret statutes as protective of companies with readings that most Democrats and liberal legal experts find highly questionable.

Throughout, Gorsuch has maintained the familiar fiction that judges only call balls and strikes, free of influence by politics or ideology. But the very nature of Gorsuch’s own nomination fight disproves that illusion. President Trump, after all, explicitly campaigned on the promise that his nominees would overturn Roe v. Wade. (At his hearing, Gorsuch claimed to be outraged by the suggestion that he ever discussed the matter with Trump.)

And let’s not forget the moment when Sen. Sheldon Whitehouse (D-R.I.) questioned Gorsuch about the $10 million in dark money poured into a campaign, run by the Judicial Crisis Network, to support his nomination. This campaign was run by the same group that had used dark money to campaign against former President Barack Obama’s nomination of Merrick Garland. Gorsuch claimed ignorance about this group’s, and its financial backers’, ardent support of his nomination. “You’d have to ask them,” he told Whitehouse, to which Whitehouse retorted, “I can’t, because I don’t know who they are.”

More broadly, Gorsuch sidestepped questions about money in politics, declining to reveal whether he agrees with the majority opinion in the Citizens United case, which struck down limits on independent spending in elections by corporations and unions. He also didn’t say whether he agrees that Congress can require disclosure of donors, only hinting that disclosure requirements might “chill expression.”

At a Judiciary Committee hearing on Gorsuch’s nomination today, Sen. Patrick J. Leahy (D-Vt.) called Gorsuch’s refusal to answer even fundamental legal questions “a blight on this confirmation process.” He added that the hearing had only “solidified” his concerns about the nominee rather than allayed them. Pointing to Gorsuch’s evasions on jurisprudence most first-year law students can recite with ease — such as Brown v. Board of Education, which struck down public school segregation — Leahy called the nominee “patronizing” and charged the jurist was committing a “disservice to the American people.”

Pressed on a range of issues, including abortion, gun control and campaign finance, Gorsuch demurred. Even his conservative supporters acknowledged he was evasive, even admitting that was the intention. As Charles Krauthammer put it on Fox News: “The whole idea is not just to be calm and collected and knowledgeable, but to be nimble. This is an exercise in obfuscation.”

But for Democrats, it was an exercise in frustration, as their constituents were denied any insight into Gorsuch’s judicial views. That’s what matters most in this fight — more than Senate procedures or devotion to the illusion that judges are apolitical. Democrats should continually remind voters that they are the reason this fight matters, and they are why Senate Democrats are going to the mat.