Papadopoulos' guilty plea is going to be more difficult for him to downplay, although the White House tried to do so on Monday.
"Today's announcement has nothing to do with the president or the campaign or campaign activity," White House press secretary Sarah Huckabee Sanders said at a White House press briefing.
Of course, that is not true. Trump named Papadopoulos as a foreign-policy adviser to the campaign. Sanders, however, dismissed him merely a "volunteer member of an advisory council that met one time."
Sanders tried to pivot to the Clinton campaign instead, alleging it "colluded" with Russian intelligence to craft the so-called "Steele Dossier." The dossier, which collected opposition research on Trump that eventually focused on his ties to Russia, was initially paid for by the conservative Washington Free Beacon website. The site is funded in large part by conservative donor Paul Singer, who was a Trump skeptic and backer of Florida Republican Sen. Marco Rubio for president.
Research for the dossier was conducted by a firm called Fusion GPS, run by two former investigative reporters. They hired Chris Steele, a former British spy turned private investigator. He has ties to U.S. intelligence and is known as a Russia expert. As a specialist, they hired him to find more information about Trump's ties in Russia that they couldn't get.
When the primaries were over, the Clinton campaign and the Democratic National Committee picked up the tab to keep the research going.
Sanders called the dossier as "false information." Some of it has been confirmed by some news outlets. Some of it is incendiary and has not been independently confirmed. Sanders dismissed the meeting at Trump Tower between Trump Jr. and Russian nationals as simply "a meeting that took place" and "routine."
It was not routine. Opposition research is, but not seeking it from foreign governments.
Sanders, though, contended the Clinton campaign's and DNC's "millions of dollars" paid for the oppo-research file (that it never used) was far worse that Trump Jr.'s meeting — or anything coming out of Monday's court documents.
"They took one meeting, and nothing came of it," she said.
Sanders also said the president had "no reaction," because "it doesn't have anything to do with us."
Not the end of the Mueller investigation
There could be more details to come either from Mueller or the congressional committees that are investigating the Russia imbroglio. Court documents indicate that Papadopoulos has met with the government "on numerous occasions to provide information and answer questions."
Sen. Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, which is also investigating Russia-Trump ties, called Monday's developments in a statement "a significant and sobering step in what will be a complex and likely lengthy investigation by the Special Counsel. That is why it is imperative that Congress take action now to protect the independence of the Special Counsel, wherever or however high his investigation may lead."
His office also said he wants bipartisan members of Congress to "make clear" to President Trump "that issuing pardons to any of his associates or to himself would be unacceptable, and result in immediate, bipartisan action by Congress."
The president has the unfettered ability to pardon anyone from federal crimes. But that only applies to federal crimes. Some officials, including Manafort, could also face charges at the state level — in New York, for example.
Warner also put the guilty plea and indictments in the context of broader developments on the Trump-Russia investigation over the last several months.
"This is just the latest in a series of undisclosed contacts, misleading public statements, potentially compromising information, and highly questionable actions from the time of the Trump campaign that together, remain a cause for deep concern and continued investigation," he said.
And there are indications that Papadopoulos is cooperating with federal agents.
"It is in the best interest of our client, George Papadopoulos, that we refrain from commenting on George's case," his lawyers, Thomas M. Breen and Robert W. Stanley, said in a short statement obtained by NPR's Carrie Johnson.
They then added: "We will have the opportunity to comment on George's involvement when called upon by the Court at a later date. We look forward to telling all of the details of George's story at that time."
Trump and other conservatives have tried to sully Mueller's name, hoping to delegitimize his findings as politically motivated. One Mueller ally, fired former FBI Director James Comey, took to his newly revealed Twitter account to seemingly — and cryptically — back up the special counsel: