When it comes to tumult, President Donald Trump’s legal team has known its fair share.

Less than a year ago, New York attorney Marc Kasowitz was helming the team—and making headlines for telling a stranger who emailed him about Rachel Maddow’s show to “Watch your back, bitch.” He departed July 21, 2017.

In the months since then, lawyers have come and gone. John Dowd, a veteran white-collar defense attorney, came aboard as lead lawyer for the president on June 16, 2017, and departed on March 22 of this year. Ty Cobb, the White House lawyer tasked with overseeing document production and interviews for special counsel Robert Mueller, is set to leave later this month. And husband-and-wife pair Victoria Toensing and Joseph DiGenova were on the cusp of joining the president’s legal team until, well, they weren’t.

But through all that, one person has remained a consistent presence: Jay Sekulow, a lawyer best known for championing social-conservative causes at the Supreme Court.

“His constitutional prowess, the confidence the president has in him, his steadiness, his lack of volatility, his ability to think strategically and communicate those strategies to the president are the reasons he’s been such an essential member of the team,” Cobb told The Daily Beast.

Sekulow gets the most attention for his media appearances; he’s a mainstay on Fox News, where he defends the president and lambasts his critics. He also hosts a daily radio show, which he spends several hours preparing for. Sekulow doesn’t have experience with white-collar criminal law, and is viewed in some corners as a television figurehead. Conservative movement leaders who know him speculated to The Daily Beast that his role on the president’s legal team must be primarily cosmetic.

But people familiar with the president’s legal team said Sekulow has played a substantial role in its actual inner workings. One source familiar with the matter said Sekulow has played an essential role in efforts to negotiate an interview between Mueller and Trump.

“There’s never been a discussion about an interview that didn’t include Jay,” the source said.

Sekulow told The Daily Beast that the president’s legal team is still working to determine its final advice for Trump on sitting for an interview with Mueller.

“There’s a full legal team in place now that’s doing a full evaluation of the case, and we’ll make a recommendation to the president,” he said.

John Dowd, formerly on the president’s outside legal team, told The Daily Beast that Mueller and his team raised 16 issues they wanted to talk about with the president, and that Sekulow and the lawyers working under him played a central role in writing up a response to those queries.

“They raised 16 issues with us they wanted to talk to the president about, and we addressed it in writing, wrote them back,” Dowd said, “And we also laid out why they were not entitled to talk to the president: Article 2, Espy, on and on.”

He said the work Sekulow and his team did writing was exemplary.

“We liked each other, we communicated, we stayed on the same page,” Dowd said. “It was terrific. I think we did an outstanding job for the president. I don’t think you can improve on what we’ve already done.”

“He’s just solid,” Dowd added of Sekulow. “He’s a good man. It was an absolute pleasure to work with him.”

Sekulow and the lawyers working under him have done research and written internal memos. They’ve also focused on the constitutional issues that may arise from the Mueller probe, particularly looking at what would happen if Mueller were to try to subpoena Trump.

“There are significant constitutional issues arising in this matter that deserve a lot of attention,” Sekulow said.

Sekulow and Rudy Giuliani, a new addition to the president’s outside legal team, have known each other for three decades and worked together on a host of issues, including advocating for the release of Andrew Brunson, a Christian pastor jailed in Turkey.

“I just received a call from the vice president’s office,” Sekulow wrote at his organization’s website in May of last year. “President Trump and Vice President Pence raised the case of American Pastor Andrew Brunson three times today with Turkey’s president, Recep Tayyip Erdoğan.”

The following month, it would be announced that Sekulow was joining President Trump’s legal team.

Trump has tweeted about Brunson’s plight and called for his release.

Beyond his years-long work with Trump on these issues, Sekulow also endeared himself to the president with his cable-news hits, where in the past year—even before joining Trump’s legal team—he has passionately defended the president. In conversations with associates and aides, Trump has positively commented on, or casually reviewed, specific clips he has caught on TV of Sekulow going after alleged corruption at the Department of Justice and FBI.

President Trump has often commented on how “sharp” he looks and sounds on live television, and has previously referred to him as one of his cable-news-ready “warriors,” according to a former White House official and another person close to Trump. The president frequently uses the term “warrior” for his favorite on-air defenders.

Dating back to at least the summer of 2011—around the same time Trump began his political ascendancy on the right as a leading figure in the racist anti-Obama birther movement—Trump began promoting and appearing on the nationally syndicated radio show Jay Sekulow Live, and taking up some of their causes on Twitter.

“Why didn’t Obama, as part of the negotiation [with Iran], free the Christian Pastor Saeed Abedini?” Trump tweeted in November 2013. (The pastor was released in January 2016.) In his tweet, Trump linked to an ACLJ post written by Jordan Sekulow, Jay’s son, denouncing President Barack Obama for leaving “Pastor Saeed behind in the vain hope that we can trust Iran.”

The following month, Trump tweeted another ACLJ post titled, “Pastor Saeed’s Wife Expresses Gratitude to Donald Trump for Raising Her Husband’s Plight.” Years later, the pastor would say that he had a vision while in solitary confinement in Iran that Trump would become president and that they would be friends.