In 1983—according to some accounts—a Honduran death squad backed by the Reagan administration tossed a Catholic priest out of a helicopter and to his death. The priest had once described himself as a “good Marxist,” and he had been the chaplain for a column of Cuban-trained communist guerillas trying overturn the country’s government.

Just three years before falling to his death, that priest met with Tim Kaine.

Today, that meeting may cause trouble for the Virginia senator. A conservative Catholic group is taking aim at Hillary Clinton’s running mate over the one part of his biography that generally appeals most to people of faith: his mission work in Honduras.

Kaine spent nine months working there with Jesuits from 1980 to 1981, and he frequently mentions his time there on the campaign trail. And he made it a focus of his speech at the Democratic National Convention.

“I got a firsthand look at a different system: a dictatorship,” he said of his time there. “A dictatorship where a few people at the top had all the power and everybody else got left out. Now that convinced me that we have got to advance opportunity for everybody, no matter where you come from, how much money you have, what you look like, how you worship or who you love.”

Discussing his experience there has been good politics; his pollster wrote in a 2005 memo that talking about his time there helped him win the Virginia governorship years ago.

Some conservative Catholics, however, are now questioning the nature of his mission work, criticizing him for praising liberation theology and meeting with a revolutionary priest. The conservative group Catholic Vote recently circulated a memo with these criticisms to its 500,000 members.

“Tim Kaine’s public record and his time in Honduras suggest that he has adopted a form of Catholicism that is at odds not only with what his church believes but with the interests of the United States,” said Brian Burch, the group’s president. “He is both in opposition to his church and in opposition to the interests of his own country.”

The Clinton campaign did not respond to a request for comment on the memo. Steve Krueger, who heads Catholic Democrats, pushed back hard against the group’s criticism of Kaine, and said the memo was “rubbish.”

“They’re basically seeking to try him in the court of public opinion because he went down to help the poor in Honduras,” Krueger said. “I find it unconscionable, actually.”

Catholic Vote pointedly criticizes Kaine for his connection to Fr. James Carney, a Catholic priest who worked with peasants in Honduras and Nicaragua, and who embraced radical politics. In a piece published Sept. 2 of this year, Kaine told the New York Times that he took a bus from Honduras to Nicaragua and then walked several miles to meet with Carney during his trip there. Kaine told the paper he spent an evening listening to the priest describe “both getting pushed around by the military and getting pushed around by the church.”

In his autobiography, To Be a Revolutionary, Carney made the case for the possibility of partially reconciling Catholicism and Marxism through liberation theology. Carney repudiated the Marxist rejection of the existence of the transcendental. But he said Marx’s criticism of religion did some good.

“Thanks partially to the Marxist criticism of religion, the Holy Spirit has finally been able to lead many present-day Christians to an understanding of the gospel of Christ and the ‘good news for the poor’ about their liberation from the yoke of exploitation,” he wrote.

He described himself as “a good Marxist,” dedicated to helping fight “the guerilla war for the liberation of Honduras.” In 1973, he renounced his American citizenship and became a Honduran citizen. The Honduran government expelled him from the country in 1979, so he moved across the border to Nicaragua, and Kaine met with him shortly after that.

The Washington Post reported that in 1983, Carney traveled with a small unit of Cuban-trained guerilla fighters as their chaplain. The paper said the group’s leader, Jose Reyes Mata, was “considered Honduras’ leading Marxist” and an ally of Che Guevara. Their aim was to destabilize the country’s government. They weren’t successful.

The Honduran Army “decimated” the insurgency, according to the Post, and Carney disappeared. The circumstances of his death still aren’t completely clear, and his body was never recovered. The New York Times reported that witnesses said a Honduran army death squad captured and killed him. His sister Virginia Smith told the National Catholic Reporter in 2003 that his family believes he was thrown from a helicopter. At the time, the Reagan administration was providing generous military assistance to the Honduran army as part of its efforts to fight communism in Central America.

So what does this tell us about Tim Kaine? Depends on who you ask.

“Fr. Carney was a priest, and he basically became a chaplain for these freedom fighters,” said Krueger. “The fact that Tim Kaine said something positive about him, to me is an indication that he sees Fr. Carney through a spiritual lens. And to me, it’s a testament to his Catholic faith.”

Catholic Vote takes a very different view.

“That Kaine made the effort to seek out and spend time with Carney is troubling,” reads the memo.

“There’s some serious questions here,” Burch added to The Daily Beast. “What was your relationship to this guy when you were down there? What did he teach you?”

Burch’s group also criticized Kaine for speaking positively about liberation theology, a strain of Catholic thought that conservative Catholics criticize as Marxist and heretical. Pope Francis has shown significantly more comfort with the current of liberation theology than his forebears.

Regardless, Catholic voters have will have substantial sway in November. Catholics are a swing bloc, and Republicans have won them in 5 of the last 11 presidential elections, as the Washington Post recently noted. Unfortunately for Trump, he’s doing terribly with them—an August survey from the Public Religion Research Institute showed Hillary Clinton is leading Trump among Catholics by 23 points.

It remains to be seen if hobnobbing in Nicaragua with a guerilla priest will help or hurt Kaine with Catholic voters. At the least, it could add a bit of an edge to his squeaky clean image.