Sen. Ron Wyden (D-OR) on Friday slammed Republicans on the Federal Election Commission for blocking an investigation into potential Russian political donations to the National Rifle Association in 2016.

“It’s inexcusable that Republican commissioners would block an investigation into whether Russian money was funneled through the National Rifle Association to help President Trump,” Wyden told Newsweek in a statement. “The blatant partisanship is appalling, undermines our democracy and leaves us vulnerable to continued interference in 2020.”

The commission deadlocked on Friday on a vote to authorize a probe of the NRA, and specifically whether it illegally accepted donations funneled through Maria Butina, who’s since pleaded guilty to acting as an unregistered Russian agent, or Alexander Torshin, the recently retired deputy governor of Russia’s central bank who worked with Butina.

Early last year, in response to an inquiry from Wyden, the NRA did acknowledge receiving foreign donations, including from Torshin to become a lifetime member, but it has asserted that none of the money was connected to a U.S. election.

Instead of investigating more thoroughly for itself, FEC Chair Ellen Weintraub said in a statement Friday, the commission and its lawyers “rel[ied] upon the NRA’s own internal review of its donations.” Weintraub described that as “hardly more thorough than searching a contributor list for the name ‘Vladimir Putin’ and calling it a day.”

The vote on further investigation was 2-2, with the commission’s two Republicans opposed.

“A foreign adversary interfered in the 2016 presidential election and the response from Republicans at every level, whether it be President Trump, congressional Republicans, or now the Republican appointees on the Federal Election Commission, has been to bury their heads in the sand or actively obstruct getting to the bottom of what happened,” Wyden said.

In her statement, Weintraub cited a January 2018 McClatchy report that, according to two unnamed sources familiar with the matter, “The FBI is investigating whether a top Russian banker with ties to the Kremlin [Torshin] illegally funneled money to the National Rifle Association to help Donald Trump win the presidency.”

“All our lawyers had to do was pick up the phone, call the FBI, and ask: Are you, in fact, investigating the Respondents for the violations alleged?” Weintraub wrote. “But when I suggested that the Commission instruct the OGC to do so, the Republican commissioners refused.”

“We still do not know the answer to this foundational, eminently knowable, question.”

One of the Republican commissioners to vote against the probe, Caroline C. Hunter, called Weintraub’s statement “long on conjecture and short on the evidence and the law,” adding: “The FEC is forbidden from investigating groups purely based on rank speculation.”