Probably no one has received more campaign donations from Russia oligarchy but Moscow Mitch--with the exception of Trump. According to Newsweek, Moscow Mitch received over 12 million in small campaign donations from 2015 to 2016 from one of two Russian oligarchies who are being investigated by the FBI. They are Blavtnic and Deripaska, Putin's close associates and are the Richest men in the UK. They also have ties to the Russian Mafia.
Deripaska has close ties to Putin and has struggled to get a visa to travel to the US because of his ties to Russian organized crime. Trump's campaign chairman, Manafort was an employee of Deripaska, and at the time Manafort joined the Trump campaign, he owed Deripaska a lot of money so, Manafort gave Deripaska a private meeting with Trump, which they deny. He was one of the dozens of Russians whose US assets were sanctions in 2018.
In April, McConnell sided with Trump and lifted the sanctions on Deripaska and other Russian oligarchies. After McConnell was given a "donation" of 200 million dollars to "invest" in Kentucky, Mnuchin allowed Deripaska to transfer almost 100 million back to Russia.