Papadopoulos admitted to prosecutors that he tried to use those connections to set up a meeting between Trump and Russian President Vladimir Putin. In April 2016, the Professor told him the Russian government had “dirt” on Hillary Clinton, including a cache of thousands of her emails. Those claims came after Russian hackers had penetrated the Democratic National Committee, but months before the cyber-attacks became public knowledge. Along the way, Papadopoulos reportedly received support and encouragement from unidentified Trump campaign officials.

“Manafort might be a bigger fish, but Papadopoulos is a bigger story,” said Steve Vladeck, a University of Texas law professor. “To me, this is the kind of plea deal that puts the c-word—collusion—back on the table.” He pointed to parts of the Papadopoulos indictment that indicated he knew about stolen Clinton campaign emails before Wikileaks began releasing them. Barrett said the indictment also sends a message to the unnamed campaign officials referenced within it. “This is a very strong signal of government interest, relevance, and consequences if they haven’t been forthcoming,” he said.

Papadopoulos’s indictment doesn’t directly prove collusion on its own, but it undermines the Trump White House’s claims of ignorance on behalf of the president and his inner circle. “Russians pursued [Papadopoulos], and he pursued Russians, and the context was the Trump campaign,” Barrett said. “It doesn’t allege anything being accomplished by this channel, but it suggests serious Russian governmental interest in contact with the Trump campaign.”

The one-two punch of the Manafort and Gates indictment, followed by the Papadopoulos plea deal just over an hour later, also suggested that Mueller was taking the hostile political climate into consideration. Before Monday, many observers thought Manafort was the likeliest subject of an expected indictment. But the Papadopoulos revelations came as a complete surprise and undermined conservative talking points.

“Not only does this suggest that Mueller is taking into account the optics and the politics of the moment, but that he’s actually trying to take advantage of them to maximize the clout of the investigation and to control the narrative,” Vladeck said.

Other filings released Monday revealed Papadopoulos was actively cooperating with Mueller’s investigation as part of his plea deal. “One assumes that the plea deal was in exchange for something” on Papadopoulos’s part, Vladeck said. “And the ‘something’ is clearly not related to the Manafort indictment. So the real question is, what exactly did Papadopoulos give up?”

Papadopoulos’s plea agreement was initially sealed. According to a motion filed in July, were its particulars publicly known at the time, they would have hampered his ability to work on behalf of investigators as a “proactive cooperator.” According to Barrett, that phrase could refer to Papadopoulos “having law enforcement-monitored meetings,” including wearing a wire or arranging “calls or emails with other subjects of the investigation who are unaware that he is cooperating with the government.”