Nick Schifrin:

Whelan visited Russia often. He supported the country's most famous soccer team. And he supported President Trump. Whelan had a profile on Russia's equivalent of Facebook.

On election night 2016, he wrote in misspelled Russian, "Onward, President Trump."

On inauguration day, he wrote, "God save President Trump."

Whelan's arrest could be connected to the U.S. government's arrest of Russian citizen Maria Butina. Last month, she pleaded guilty to acting as an agent of the Kremlin to influence U.S. politics. She had met with Republicans such as former Wisconsin Governor Scott Walker.

Whelan's family insists he wasn't working for the U.S. government.

So, why did Russia arrest Paul Whelan? And how likely is it that he is a spy, as the Russians claim?

For that, we turn to John Sipher, a 28-year veteran of the CIA who was based in Moscow in the 1990s. He subsequently oversaw operations against Russian intelligence services and is now with the consulting firm CrossLead.

John Sipher, thank you very much for being here.