Special counsel Robert Mueller increasingly views President Donald Trump’s trip back from the G-20 summit in Europe this July as a critical moment in his investigation. And as part of an attempt to uncover just what happened on that fateful flight, his team is expected to question several White House officials. Among them will be the president’s close adviser Hope Hicks.

People familiar with the probe tell The Daily Beast that Hicks—the longtime Trump aide who is currently interim White House communications director—likely has information that will interest Mueller regarding Donald Trump Jr.’s initial claim that his meeting with the Kremlin-linked lawyer Natalia Veselnitskaya was just about adoption.

“No doubt in my mind she is going to be a witness,” a source familiar with the Mueller probe told The Daily Beast.

On Friday, The Washington Post reported that Hicks wasn’t alone on Mueller’s radar. Former White House chief of staff Reince Priebus, former press secretary Sean Spicer, White House counsel Don McGahn, McGahn aide James Burnham, and Kushner aide and White House spokesman Josh Raffel are also expected to be questioned.

In a reflection of how serious the administration is taking the matter, sources tell The Daily Beast there are currently efforts underway to organize a legal defense fund for White House staffers. Such a fund would help cover the legal bills associated with Mueller’s probe, which are expected to be large. A Washington white collar attorney told The Daily Beast that everyone questioned by Mueller will likely need to retain counsel. Those lawyers will likely bill between $500 and $1000 per hour.

In most cases, third parties can pay for federal workers’ legal defense funds. As The Daily Beast reported in August, Paul Manafort and Michael Flynn—two targets of the probe—are already facing significant financial strain because of high legal bills.

It’s unclear if Hicks has retained counsel as well. She, and the White House comms shop, did not return repeated requests for comment on this story. Officials spoke to The Daily Beast on the condition of anonymity to discuss sensitive matters.

Hick’s potential targeting by Mueller also underscores the aggressive direction his probe is increasingly taking. Outside of direct family members, she is, perhaps, closest to Trump. Hicks was on the Air Force One flight back to the United States after the G-20 summit and played a role in drafting the statement on Trump Jr.’s June 2016 meeting between Veselnitskaya and Jared Kushner, Paul Manafort, and Trump Jr.

That statement, which was put together by senior White House officials—including the president himself—turned out to be wildly misleading. Hicks reportedly encouraged a more transparent initial approach in describing the facts of the Trump Tower meeting. But she was ultimately overruled. When The New York Times first reported the existence of the meeting, a statement in Trump Jr.’s name downplayed its significance.

“It was a short introductory meeting,” Trump Jr.’s initial statement said. “I asked Jared [Kushner] and Paul [Manafort] to stop by. We primarily discussed a program about the adoption of Russian children that was active and popular with American families years ago and was since ended by the Russian government, but it was not a campaign issue at the time and there was no follow up.”

Minutes before The New York Times published a subsequent story on the meeting, Trump Jr. publicly released emails showing that he, in fact, enthusiastically accepted a meeting where he was promised damaging information about Clinton from officials acting on behalf of the Russian government.

Mueller and his investigators are now looking to question White House staffers who were on Air Force One when the statement was drafted.

Hicks takes pains to avoid the media spotlight. She rarely speaks with reporters on the record and never acts as a White House media surrogate. She has worked closely with Trump for years, and won his trust long before he announced his presidential bid. She is one of the handful of people the president truly trusts, outside of his immediate family.

One White House adviser who spoke with Hicks recently said she expected to hear from Mueller.