Donald Trump’s second of three campaign chiefs, Paul Manafort, announced through a spokesperson today that he is planning to formally register as a foreign agent. Manafort has worked, in one capacity or other, for foreign politicians since at least his mid-1980s advocacy on behalf of Angolan guerrilla leader Jonas Savimbi, a onetime Maoist who was trying to rebrand himself as a freedom fighter for the Reagan era.

Foreign agent registration means, in essence, that you are an official lobbyist for a foreign government — there are well over 1,000 registered foreign agents in Washington.

But while it’s not entirely clear what about Manafort’s business arrangements have changed to lead him to conclude that he needs to formally register, it likely has something to do with the increased scrutiny Manafort is receiving as a result of his ties to both Trump and the government of Russia.

Manafort went to work for Trump’s campaign without pay last summer, after Corey Lewandowski’s June 2016 ouster in the wake of his physical altercation with a Breitbart reporter. Manafort was an old associate of Trump’s, having worked with him on casino-related political matters years before the launch of the businessman’s presidential campaign, and his hiring was initially seen as a somewhat desperate reach to hire an old-time GOP operative who hadn’t really been in the game in years.

But Trump’s puzzling affection for Russian dictator Vladimir Putin — and Putin’s subsequent efforts to intervene in the US presidential campaign on Trump’s behalf — cast Manafort’s work in a somewhat different light. One of his major clients in recent years had been the Russia-friendly Ukrainian political party whose ouster from power set off the Russian invasion of Crimea and eastern Ukraine.

Manafort has, consequently, figured extremely prominently in various lines of speculation about ties between Trump and Russia.

New evidence emerged Wednesday confirmed earlier reports that Manafort was paid millions by the pro-Russian Ukrainian party while it was in office, and reporting in late March showed that in the mid-aughts Manafort pitched Russian oligarchs on a scheme to “greatly benefit the Putin government” through pro-Russian advocacy in the West.

Under the circumstances, it’s natural that investigators looking into possible collusion between the Trump campaign and the Russian government would take an interest in Manafort.

Manafort himself maintains that he’s done nothing wrong. But a person under that kind of scrutiny needs to make sure he’s not also somehow violating of the letter of the Foreign Agents Registration Act or otherwise skirting the law.