For most of his life, billionaire Len Blavatnik put few of his vast resources into US politics. That changed in 2015.

Since then, the oligarch, a US citizen who was born and raised in the former Soviet Union and made his fortune in Russia, has donated more than $6 million to Republicans, according to Federal Election Commission data cited by the Dallas Morning News, plus $1 million to Donald Trump’s inaugural committee, and several hundred thousand dollars to Democrats, including relatively small sums to senators Kamala Harris and Ron Wyden, FEC filings show.

The question of Russia-linked money entering US politics has been of interest to law enforcement and congressional investigators since reports of Moscow’s meddling in the 2016 presidential election surfaced that year. Now, numerous ties between the Kremlin and people in the Trump orbit have been revealed, and Russian graduate student Maria Butina has pleaded guilty to trying to infiltrate the Republican party as a foreign agent for Russia.

Quartz’s reporting shows that, during at least part of the time Blavatnik was stepping up his GOP donations, one of his many companies was partnered with a firm that was reportedly part-owned by a then-official in the Russian government. He also was in business with two other oligarchs now sanctioned by the US government. (Blavatnik’s contributions are legal—he became a naturalized US citizen in 1984.)

Asked in September 2017 by ABC News about a report that US special counsel Robert Mueller was looking into donations to Trump’s inauguration fund by Blavatnik and other Republican donors with Russian ties, Adam Schiff, now chair of the House Intelligence Committee, said, “if there were those that had associations with the Kremlin that were contributing, that would be of keen concern.”