One of California Rep. Dana Rohrabacher’s Democratic challengers is calling on him to return money from former Donald Trump campaign chairman Paul Manafort, who was indicted on charges related to the Russia investigation on Monday.

Hans Keirstead, a stem cell researcher who is one of several candidates challenging the Republican incumbent, said Manafort’s contribution to Rohrabacher’s campaign is “tainted.”

“It’s alleged that Manafort improperly received funds from foreign interests, and committed various money laundering and other fraud crimes,” Keirstead said in a statement. “His money is tainted. Rohrbacher should give back the Russian tainted money as soon as possible.”

Manafort and associate Rick Gates were indicted on Monday for conspiracy against the United States, money laundering and other charges related to business dealings. 

The charges were the first related to the investigation led by special counsel Robert S. Mueller III in his probe of Russian meddling into the 2016 elections. Manafort turned himself on Monday.

Manafort made two campaign contributions of $1,000 to Rohrabacher — one for the primary campaign and one for the general election — in 2013 when Manafort was representing pro-Russian Ukrainian clients.

Rohrabacher Press Secretary Ken Grubbs wouldn’t comment on Keirstead’s suggestion except to say, “The congressman advises both his political opponents and the media to observe the American principle of presumption of innocence.”

Rohrabacher has been called “Putin’s favorite congressman,” referring to Russian President Vladimir Putin and the congressman’s support of improving relations between Russia and the United States.

Rohrabacher’s 48th District seat is rated Tilt Republican by Inside Elections with Nathan L. Gonzales.