Manafort’s resignation comes only hours after the Associated Press reported that his firm run had directed a “covert” lobbying operation on behalf of Ukraine’s then-ruling political party, and tried to sway U.S. public opinion in favor of the country’s pro-Russian government. This work was conducted without registering as foreign agents, as required by federal law, the AP reported.

“This morning Paul Manafort offered, and I accepted, his resignation from the campaign,” Trump said in a statement. “I am very appreciative for his great work in helping to get us where we are today, and in particular his work guiding us through the delegate and convention process. Paul is a true professional and I wish him the greatest success.”

He is the second campaign manager to resign from the Trump campaign.

Trump had tried to distance himself from the growing row earlier in the week by hiring Breitbart chairman Steve Bannon and pollster Kellyanne Conway to run the campaign, but ultimately Manafort’s past connections proved too toxic even for a candidate who has seemed largely indifferent to controversy during his campaign run.

The AP said Manafort and his deputy, Rick Gates, channeled over $2 million into efforts to curry favor with U.S. officials and journalists, pushing the broadly pro-Russian agenda of the the party of then-President Viktor Yanukovych (the ‘Party of the Regions’).

Contrary to the requirements of the 1938 Foreign Agents Registration Act, the AP said, they never disclosed their work on behalf of the Ukrainian government, even though Gates, then working for Manafort’s consulting firm, personally directed the work of two prominent Washington lobbying firms in the matter. Manafort declined to comment to the AP but told Yahoo News that the AP’s version of events was “wrong.”

The development caps a week of tumult for the Trump campaign, in which the GOP nominee has had to field increasing criticism for his apparent chumminess with Russia and its proxies.

Earlier this week, Manafort had tried to deny as “unfounded, silly and nonsensical” claims that he had received cash payments worth up to $12.7 million from a “black ledger” controlled by Yanukovych’s “Party of the Regions.” However, the Ukrainian lawmaker Serhiy Leshchenko backed up those claims Friday, showing that a certain Vitaly Kalyuzhny had signed nine times for receipt of payments designated for Manafort. The payments appear not to have been declared to local authorities at the time, which would also make them illegal under Ukrainian law.

Kalyuzhny is a pivotal figure in a complex web of lobbying that also has implications for the campaign of the Democratic Party’s presidential nominee Hillary Clinton.

According to the New York Times, Kalyuzhny was a founding board member of a non-governmental organization in Brussels that channeled over $1 million to Washington in an effort not only to U.S. support for Yanukovych’s government, but also to trash the pro-Western Yulia Tymoshenko, who lost the 2010 presidential run-off with Yanukovych and was then jailed on corruption charges after a trial widely condemned as rigged and politically motivated.

Kalyuzhny’s ‘European Center for a Modern Ukraine’, based in Brussels, hired the Podesta Group to get Yanukovych’s message across in DC. Podesta was co-founded by John D. Podesta, who is now chairman of Clinton’s campaign (his brother Tony has taken over the running of the firm).

The AP said the emails it had obtained show Gates personally directed two Washington lobbying firms, Mercury LLC as well as Podesta, between 2012 and 2014 to set up meetings between Ukraine’s foreign minister, Leonid Kozhara, and senators and congressmen on influential committees involving Ukrainian interests. Gates noted in the emails that Kozhara expressly wanted to avoid using his own embassy in the U.S. to help coordinate the visits.

CORRECTION: This article has been updated to correct the name of Kellyanne Conway.