The alleged crimes of Manafort and Gates appear to predate their involvement in the Trump campaign, allowing the White House to claim that Mueller has not yet come up with any evidence of collusion.
But the charges hint at far more to come. Manafort in particular had longstanding ties to the Kremlin at a time when several people in the Trump campaign were at least actively discussing working with the Russians to undermine Hillary Clinton.
It would be remarkable if no one tried to use Manafort's connections - and Mueller may not even have to prove that they did.
Many Washington commentators believe his real intention is to "flip" Manafort and Gates, by squeezing them so tight on the criminal conspiracy charges that they testify against others in the Trump campaign in exchange for leniency.
That in turn puts intense pressure on everyone else under investigation.
Papadopoulos' guilty plea has even more disturbing implications for the White House.
During the election campaign, the FBI says he repeatedly tried to arrange a meeting between Trump and the Russian government, which he was told had damaging information about Clinton.
In scenes reminiscent of spy fiction, the FBI claims the go-between was London-based Professor Joseph Mifsud, who arrived at one meeting with a woman posing as Vladimir Putin's niece.
Papadopoulos has now admitted lying to the FBI by claiming the meetings took place before the campaign and is described as a "proactive cooperator".
In other words, it is understood he agreed to wear a wire to get incriminating statements from senior figures in the Trump campaign.
Since he was arrested three months ago and Mueller has only now agreed to unseal his guilty plea, it seems likely that Papadopoulos has proved very valuable to the investigation.
Mueller still has a long way to go to prove that Trump conspired with the Russians to win the election.
There is also no doubt that both sides played hardball - the Democrats paid a former British spy to dig up unpleasant and still unproven claims about Trump's personal life.
But the high level of Russian sabotage in the US election is already clear and deeply disturbing for American democracy.
Facebook admitted to Congress this week that Russian agents had pushed inflammatory posts about race, religion, gun rights and gay issues to 126 million users in an election dominated by themes of hate and fear.
If Mueller's investigation succeeds in linking Trump's campaign to Russia's dirty tricks, the president is in deep trouble.
