Lawmakers from both parties have also doubled down on their defense of Mr. Whelan.
On Friday, Senator Marco Rubio, Republican of Florida, posted on Twitter a call for Mr. Whelan’s release, and Senator Gary Peters, Democrat of Michigan, said that Mr. Whelan’s detention was “a political stunt by the Russians.”
“Enough is enough: The Russian government needs to let Paul go,” Mr. Peters said.
Secretary of State Mike Pompeo has raised the matter with Russia’s foreign minister, Sergey V. Lavrov. But, perhaps to avoid escalating tensions with Moscow, the Trump administration has not classified Mr. Whelan as wrongfully detained, meaning he is not considered a hostage.
In September, Mr. Peters urged the White House to have the special presidential envoy for hostage affairs help secure Mr. Whelan’s release.
If a special envoy can be used to secure the release of the rapper ASAP Rocky, surely one can be used for Mr. Whelan, congressional staff members have said.
And Ms. Whelan said that without the help of the government’s hostage team establishing a “fusion cell,” it was hard to coordinate the government’s efforts. By visiting Washington each month, she said, she was trying to improve the flow of information among departments and Congress about her brother’s situation.
“Of course the difficulty is that I don’t work within the government and I can’t make things happen,” she said.
Mr. Whelan, a former Marine, was seized last December and accused of espionage-related crimes. At a court appearance this week, on Christmas Eve, he held up a sign reading, “I remain innocent! No espionage! No evidence!” At earlier court appearances, he has also repeatedly declared his innocence.