The list of Trump associates to come under Robert Mueller’s magnifying glass may soon include the president’s longtime assistant, Rhona Graff. Amid the escalating Justice Department probe into Kremlin interference in the 2016 election and multiple congressional investigations, lawmakers reportedly want to speak with Graff, who has served as Donald Trump’s gatekeeper for decades.

Graff, a senior vice president at the Trump Organization, first entered the roving spotlight in the Russia saga when Donald Trump Jr. shared a string of e-mails related to his now-infamous meeting with a Kremlin-connected lawyer at Trump Tower last summer, which has emerged as a key focus in the various Trump-Russia investigations. “I can also send this info to your father via Rhona but it is ultra sensitive so wanted to send to you first,” Rob Goldstone, the British publicist and Trump family business partner who helped arrange the controversial meeting, wrote in an e-mail to the eldest Trump son. The exchange raised the possibility that the president himself might have been informed of the alleged Russian government effort to assist his campaign.

It is not apparent from those e-mails whether Goldstone ever connected with Graff about the Trump Tower meeting—one question congressional investigators reportedly hope to answer. “Since her name is in the e-mail, people will want her to answer questions,” Peter King, a Republican member of the House Intelligence Committee, told ABC News. “If you go into Trump Tower, you’re going to mention her name.” Eric Swalwell, who also serves on the House Intelligence Committee, echoed the sentiment. “I think we should hear from every individual who is mentioned in the Don Jr. e-mail chain to understand what was happening,” the California lawmaker said. Graff is not accused of any wrongdoing.

Senate Intelligence Chairman Richard Burr demurred when asked whether his own committee would be seeking information from Graff. But it is unsurprising that Congress would want to talk to Trump’s right hand, who has played a pivotal role in his businesses for years. Graff has reportedly maintained her position in Trump’s orbit even since he became president, suggesting that she could be a wealth of knowledge for investigators.

Lawmakers’ interest in Graff is likely to infuriate Trump. Last month, the president—who has continually dismissed the Russia investigation as a “witch hunt” orchestrated by allies of Hillary Clinton as an excuse for losing the election—said that special counsel Robert Mueller would be crossing a line if he began to investigate the Trump family, their finances, and the Trump Organization in a way that exceeded the initial scope of the Russia probe. Calling Graff to testify before Congress, or otherwise requesting information from her, might fall into that category.

News of Graff’s involvement comes as Mueller’s investigation rapidly escalates. At the end of last month, the F.B.I. raided the home of Paul Manafort, Trump’s former campaign chairman, for documents related to the Trump-Russia probe. Trump’s lawyer John Dowd blasted the aggressive tactic on Thursday, characterizing it as an “extraordinary invasive tool” that he argued was “employed for its shock value to try to intimidate Mr. Manafort and bring him to his [knees].” Investigators are also reportedly seeking information from a handful of Manafort’s associates, including his estranged son-in-law Jeffrey Yohai, fueling speculation that the F.B.I. might be trying to pressure Trump allies to turn cooperating witnesses. On Thursday, Manafort switched up his legal team, opting for a Washington firm that reportedly specializes in financial investigations. “Mr. Manafort is in the process of retaining his former counsel, Miller & Chevalier, to represent him in the office of special counsel investigation. As of today, WilmerHale no longer represents Mr. Manafort,” Manafort spokesman Jason Maloni said in a statement.