Alex Brandon/AP

Former special counsel Robert Mueller broke new ground, perhaps for the first time, when he criticized Trump for embracing WikiLeaks during the 2016 campaign, and touting the hacked Democratic emails they released before the election.

Asked to react to Trump’s behavior, Mueller said:

“Problematic is an understatement, in terms of what it displays, in terms of giving some hope or some boost to what is and should be illegal activity.”

What he's talking about: The “illegal activity” likely refers to the hacking of Democratic emails by Russian intelligence officers. They hacked the Democratic National Committee and Hillary Clinton’s campaign chairman, then funneled the stolen emails to WikiLeaks, according to the Mueller report. WikiLeaks later published many of the emails.

Trump touted the new leaks at nearly every stop on the campaign trail in the final weeks of the race, sometimes reading directly from emails at his rallies and seizing on thinly sourced conspiracy theories.

Democrats have condemned Trump for doing that, saying he was openly embracing Russian meddling. For the first time, Mueller agreed with that assessment when he said Trump’s actions were “problematic.”

To be clear, it is not a crime to read aloud from news stories or hacked emails that are posted online. The crimes were committed by the Russians who hacked the emails. But by embracing WikiLeaks, candidate Trump aligned with Russia’s goals of disrupting the campaign and weakening Clinton’s chances of winning.

Almost all of the Democratic candidates running for the 2020 campaign have pledged that they won’t use any hacked materials during the campaign to attack their opponents. Trump has not made this promise and has publicly suggested that he’s more than willing to accept help from foreign governments in 2020.