Lawyers for the CIA officer whose whistleblower complaint helped ignite an impeachment inquiry into President Trump have asked Congress whether their client could submit testimony in writing instead of appearing in person, according to people familiar with the matter.

The request reflects concerns about whether the whistleblower could testify to Democrats and Republicans without revealing his identity, and fears that doing so would lead to it being publicly leaked, jeopardizing his personal safety. The intelligence committees haven’t yet responded to the inquiry about potential written testimony, the people said.