President Obama on Friday sharply criticized Republicans who say they approve of Russian President Vladimir Putin, with Obama saying that “Ronald Reagan would roll over in his grave” if he saw so many in the GOP expressing fondness for leaders in Moscow.

Speaking to reporters at his final press conference of 2016, Obama stopped just shy of explicitly blaming Putin for ordering Russian hacks of Democrats during the election campaign but left no doubt who’s to blame.

“Not much happens in Russia without Vladimir Putin,” Obama said. “This is a pretty hierarchical operation. Last time I checked, there’s not a lot of debate and democratic deliberation, particularly when it comes to policies directed at the United States.”

The president pointed to a public opinion poll that he said showed 37 percent of Republicans have a favorable view of Putin, blaming the “fierceness of partisan battle” in the United States for driving Americans into the arms of a historic foe.

“Over a third of Republican voters approve of Vladimir Putin, the former head of the KGB,” he said. “Ronald Reagan would roll over in his grave.”

And Obama said Moscow can only undermine the U.S. if Americans let it.

“The Russians can’t change us or significantly weaken us,” he said. “They are a smaller country, they are a weaker country, their economy doesn’t produce anything that anyone wants to buy except oil and gas and arms. They don’t innovate. But they can impact us if we lose track of who we are. They can impact us if we abandon our values.”