Sen. Ted Cruz is obnoxious. Sen. Marco Rubio is nice. That’s why so many Republican politicians, donors, and party leaders want the senator from Florida, not the senator from Texas, to be the Republican nominee for president. They think Rubio would attract more voters than Cruz in a general election, and polls suggest they’re right. But the polls and pols miss an important factor: Tactically, Cruz is smarter than Rubio. That difference is becoming clearer as the candidates grapple with the death of Supreme Court Justice Antonin Scalia.

In his three decades on the court, Scalia cast the deciding vote in dozens of cases. His departure raises the prospect that a new liberal justice could supply the fifth vote to overturn these rulings. A Republican presidential candidate who wants to scare and mobilize conservative voters could choose to highlight any of the issues at stake, from contraception to campaign finance to the death penalty. Over the weekend, Cruz and Rubio chose their issues. Rubio picked gay marriage. Cruz picked guns.

At the start of Saturday night’s debate in Greenville, South Carolina, the candidates were asked for their thoughts about Scalia. Rubio praised the late justice’s “dissent on Obergefell,” the 2015 case that struck down laws against same-sex marriage. In his closing statement, Rubio added, “We’re going to be a country that says that marriage is between one man and one woman.” On Fox News Sunday, he repeated that “marriage is between one man and one woman” and that “Obergefell should be overturned.”

Cruz took a different tack. In a statement on Saturday afternoon, he said Scalia had “authored some of the most important decisions ever, including District of Columbia v. Heller, which recognized our fundamental right under the Second Amendment to keep and bear arms.” In the debate, Cruz opened with a stark declaration: “We are one justice away from a Supreme Court that will reverse the Heller decision, one of Justice Scalia’s seminal decisions, that upheld the Second Amendment right to keep and to bear arms.” He repeated that warning later in the debate, in a post-debate interview, and on the Sunday morning talk shows. On ABC’s This Week, Cruz pleaded:

Let me say something in particular to the veterans of the state of South Carolina. … Your Second Amendment rights are hanging in the balance. Justice Scalia, one of his biggest opinions was the Heller decision. It was 5-4, upholding the individual right to keep and bear arms. If an additional liberal justice goes to the court, we’re one justice away from the Second Amendment being written out.

Why does Cruz talk about Heller while Rubio talks about Obergefell? It’s not because of their records: Both men oppose gun control and same-sex marriage. It’s because Cruz is smarter. Obergefell is a silly choice. Scalia wasn’t even in the majority in that case, so losing his seat to a liberal justice wouldn’t change the outcome. But the bigger problem with Obergefell is that gay marriage is now a losing issue for Republicans. Polls show that most Americans favor legal recognition of same-sex marriage, reject state discretion on the issue, support the court’s ruling, and oppose overturning it.

Heller is a much better choice. Scalia wasn’t just the deciding vote. He wrote the opinion. Americans support his position and the right it protected. In a CNN/ORC poll taken in June 2008, just before Heller, 67 percent of Americans said the Second Amendment guaranteed “that each individual has the right to own a gun,” not just “the right of citizens to form a militia.” In a 2012 Pew poll, 67 percent opposed “banning the possession of handguns except by law enforcement officers.” In a CNN/ORC poll, also taken in 2012, 89 percent opposed “preventing all Americans from owning guns.”

The public does support some restrictions on firearms. But the intensity is on the pro-gun side. Four months ago, Gallup asked registered voters whether they would “only vote for a candidate who shares your views on gun control,” consider the issue “as just one of many important factors when voting,” or treat it as a minor issue. Thirty-four percent of conservatives said gun control was a deal-breaker, compared with 22 percent of liberals. Forty percent of voters who wanted looser firearm laws said the issue was a deal-breaker, compared with 21 percent of voters who preferred stricter laws.

Why does opposition to gun bans outpoll opposition to gay marriage? Because legalizing my marriage doesn’t mess with yours. But a gun ban does mess with you. People who own guns, want guns, or believe they should have the right to a gun don’t like being told they can’t have one. To paraphrase Charlton Heston’s famous vow, you will pry their weapons from their cold, dead hands.*

This is what liberals don’t understand about gun control: The right to a firearm feels as fundamental to conservatives as the right to abortion feels to liberals. It’s the same pro-choice logic: I might not own a gun. I might not even expect to need one. But that’s my decision, not yours. I have a right to defend myself, and it’s none of the government’s business. Don’t like guns? Don’t buy one.

The connection between guns and abortion, between the right to bear arms and the right to decide whether to bear a child, goes back decades. It’s one reason why I called my book on abortion politics Bearing Right. In 1986, a team of strategists in Arkansas, led by pollster Harrison Hickman and Planned Parenthood activist Brownie Ledbetter, orchestrated a ballot-measure campaign that reshaped pro-choice politics nationwide. Their key insight was to link left- and right-wing libertarianism. In March 1986, three months before Scalia was nominated to the Supreme Court, Hickman and Ledbetter wrote the seminal poll question: “The government is threatening to take away our right to own a gun and telling us where to send our children to school, and now they want to say that women can’t have abortions—even if they’re raped.”

Twenty-two years later, Scalia wrote Heller. The opinion earned him one of the worst insults of his career. Two judges appointed by President Reagan—Richard Posner and J. Harvie Wilkinson—dismissed Heller as a right-wing version of Roe v. Wade, concocted from ambiguous texts and imposing the views of a few justices on the states. But the political resonance between Roe and Heller wasn’t fully realized until 2015, when Cruz—who, as solicitor general of Texas, had written an amicus brief for 31 states in Heller—made the vulnerability of the right to firearms a rallying cry in the presidential election.

Four months ago, Cruz warned an audience in Iowa: “One more liberal justice, and our right to keep and bear arms is taken away from us by an activist court.” He has repeated that warning many times in Iowa and New Hampshire. Last month, Cruz told CNN:

I represented 31 states in the Heller case, which upheld the individual right to keep and bear arms. You know what Barack Obama’s position is? That there is no individual right to keep and bear arms whatsoever under the Constitution. … Hillary Clinton, for example, has said she will put Supreme Court justices on the court who will overturn Heller. And if Heller is overturned … there were four justices who said that there is no individual right to keep and bear arms whatsoever, that it is only a collective right in the militia, which is fancy lawyer talk for a nonexistent right. … [If] Hillary Clinton gets one more Supreme Court justice, what it would mean is, the Supreme Court would say you and I and every individual American have no constitutional right under the Second Amendment at all, and either the federal government or a state government could make it a crime to possess a firearm.

In South Carolina, Cruz is doubling down on that message. At a rally on Monday, he spent more than 10 minutes talking about Scalia and the stakes of losing that seat on the court. He devoted two minutes just to Heller and guns. “The four dissenters in Heller said the Second Amendment does not protect any individual right to keep and bear arms,” Cruz told the crowd. “One more liberal justice, and the Supreme Court will overrule Heller. … What that would mean is, the federal government or any state or local government could make it a crime for law-abiding citizens to possess a firearm.”

Meanwhile, at a rally two hours away, Rubio spent barely one minute of his speech talking about the court. He never mentioned guns, and when a questioner asked about Scalia, Rubio said the important thing was judicial philosophy, not specific issues.

It’s possible that Rubio will end up as the Republican nominee. But if he does, it will be on the strength of his charm, not his acumen. To win the general election, Rubio would need to think more like Cruz, choosing issues that fit the moment and serve his candidacy. When it comes to the Supreme Court, that issue isn’t marriage. It’s guns.

*Correction, Feb. 16, 2016: This article originally misspelled Charlton Heston’s first name.