One year ago today, the U.S. Department of Justice released special counsel Robert Mueller’s report on Russian interference in the 2016 election.

Mueller’s report is the single most damning document ever released about a sitting president, which is why President Donald Trump and his allies have spent the past year sowing doubt about its conclusions—including by effectively extorting multiple foreign governments to give them dirt on the investigators in exchange for help from the U.S. government. In almost 450 pages, Mueller lays out in extraordinary detail how Trump colluded with a hostile foreign power’s “sweeping and systematic” attack on American democracy, then brazenly obstructed justice to ensure that he wouldn’t be caught.

The Trump campaign colluded with the Russian government to undermine American democracy and win the 2016 election.

Throughout the campaign, Trump’s personal lawyer Michael Cohen was communicating with Russian officials about secret efforts to develop a Trump Tower in Moscow.

In April 2016, Kremlin-linked Maltese professor Joseph Mifsud told Trump campaign aide George Papadopoulos that Russia planned to anonymously release emails stolen from Trump’s political opponents.

When an emissary for a Russian oligarch offered “official documents and information that would incriminate Hillary [Clinton]” as “part of Russia and its government’s support for Mr. Trump,” Donald Trump Jr. jumped at the opportunity and arranged a meeting, bringing along Trump’s son-in-law Jared Kushner as well as campaign chairman Paul Manafort.

Manafort and his deputy Rick Gates shared polling data and campaign strategy with suspected Russian intelligence operative Konstantin Kilimnik on the understanding that Kilimnik would pass the information along to an oligarch close to Putin. (Gates told Mueller he considered Kilimnik a Russian “spy,” but Manafort denies having believed the same.)

According to testimony during Mueller’s investigation, after WikiLeaks began releasing the emails Russia had stolen, Trump instructed his campaign to establish backchannels to get advance notice of what was coming next, most famously through Trump’s longtime political adviser Roger Stone.

During the transition, Michael Flynn, who Trump had tapped to become his national security adviser, conspired with the Russian ambassador to the United States to undermine sanctions that the Obama administration had placed on Russia as a punishment for its interference.

All in all, the Trump campaign and transition team had at least 272 known contacts and at least 38 known meetings with Russia-linked operatives while the Kremlin was actively attacking American democracy—and sought to cover up each and every one. Cohen, Papadopoulos, Manafort, Stone, and Flynn have all since pleaded guilty or been convicted of lying to investigators about their actions.

Trump tried to interfere with the investigation to prevent his and his top advisers’ crimes from becoming public.

In his report, Mueller specifically said that, though DOJ guidelines precluded him from indicting a sitting president, he could not unequivocally state that Trump was not guilty of obstruction of justice. More than 1,000 former federal prosecutors agreed, signing onto a letter stating that if Trump were not president, he likely would have been prosecuted for obstruction of justice.

Damning as the Mueller report is, it leaves several key questions unanswered, including:

Why didn’t Mueller investigate Trump’s finances beyond Trump Tower Moscow? Did Deputy Attorney General Rod Rosenstein block him from doing so, as a source in the government reported told The Washington Post’s David Ignatius in February 2019?

What was the result of the counterintelligence portion of the investigation—whose findings are still secret, even from Congress?

Did Russia surreptitiously funnel money into Trump’s 2016 campaign, as they have for Kremlin-aligned politicians in Europe?

What happened to the 12 redacted criminal referrals listed at the end of Mueller’s report, as well as House Intelligence Committee Chairman Adam Schiff’s (D-CA) criminal referral for Trump adviser Erik Prince?

Mueller’s report was an impeachment referral for both collusion and obstruction of justice. With Trump already colluding again, it is vital that the American public remember just how damning the Mueller report truly is.