Rep. Adam Schiff, D-Calif., chairman of the House Intelligence Committee, speaks to reporters Thursday on Capitol Hill. Andrew Harnik/Associated Press

WASHINGTON — Lawmakers face a delicate task as they try to obtain testimony from the person who blew the whistle on President Trump and Ukraine. They say they are concerned for that person’s safety, especially in light of the president’s tweets suggesting he believes the person’s actions could be treasonous.

The House and Senate intelligence committees have been in negotiations for more than a week with the whistleblower’s attorneys and Acting Director of National Intelligence Joseph Maguire to ensure the person is protected if he or she testifies behind closed doors. The person is willing to speak to Congress, the attorneys say, but only if Maguire can ensure anonymity and safety from reprisal.

“Unfortunately, we expect this situation to worsen, and to become even more dangerous for our client and any other whistleblowers, as Congress seeks to investigate this matter,” Andrew Bakaj, one of the whistleblower’s attorneys, wrote in a letter to Maguire on Saturday.

Bakaj referred to Trump’s comments that he wants to know who the whistleblower is, and that people who gave the person information are “close to a spy.”

Trump said last week: “You know what we used to do in the old days when we were smart? Right? With spies and treason, right? We used to handle them a little differently than we do now.”

Asked Monday whether he knows the whistleblower’s identity, Trump replied, “We’re trying to find out,” even though the person’s identity is protected by the Whistleblower Protection Act.

In a statement Sunday, Bakaj and other lawyers for the whistleblower said they are working with both committees and that no time and date has yet been set for testimony. He said the committees agree that “protecting the whistleblower’s identity is paramount.”

House Intelligence Committee Chairman Adam Schiff, D-Calif., said Sunday on NBC’s “Meet The Press” that the whistleblower would appear “I hope very soon.”

The safety concerns underscore the unprecedented nature of the whistleblower’s complaint. Democrats have made the complaint the center of their impeachment investigation, raising questions about whether the person will be able to remain anonymous.

“I think we all have to be concerned about leaks,” Virginia Sen. Mark Warner, the top Democrat on the Senate intelligence panel, said in an interview with The Associated Press on Monday. Warner is encouraging his Republican colleagues to speak out against the president’s comments about the whistleblower, which were repeated in various iterations in tweets over the weekend.

Warner said the threats will produce a chill among whistleblowers and others who might want to expose wrongdoing.

“I’ve already heard from folks in the intelligence community. They’re worried,” he said.

Schiff said he will do “everything humanly possible” to make sure the person’s identity will be kept secret if lawmakers do meet the person face to face.

“The president has suggested that people like this whistleblower should be treated the way that we used to treat spies and traitors,” Schiff said. “And we used to execute spies and traitors. There’s no messing around here.”