As the probe wears on, the fundamental legitimacy of Trump’s presidency hangs in the balance: Did his campaign conspire with Russia to undermine Hillary Clinton and win the election?

Here, the most significant revelations the country has learned since Mueller began his probe—revelations that could eventually answer that question.

Jared Kushner Proposed a Secret Backchannel to Moscow

In late May 2017, The Washington Post reported that Jared Kushner, Trump’s son-in-law and senior adviser, was willing to go to extraordinary lengths to establish a secret line of communication between the Trump team and Russian government officials during the presidential transition after the 2016 election. As part of a series of meetings he held with foreign officials during that period, Kushner spoke with Russia’s then-ambassador, Sergei Kislyak, in December and floated the possibility of setting up a secure channel. He also wanted those talks to take place in Russian diplomatic facilities in the U.S., which would essentially conceal future interactions from the American government, according to The Post. A surprised Kislyak relayed Kushner’s offer back to Kremlin officials, in conversations that were picked up as part of the intelligence community’s routine eavesdropping of monitored foreign agents.

Kushner explained in a statement prepared for the congressional intelligence committees investigating potential collusion that he had simply been wondering aloud whether such a channel existed, so that the incoming administration could securely discuss their military options in Syria with the Russians. But he did not initially disclose the Kislyak meeting to U.S. officials during his background check—the White House only acknowledged it after news outlets reported on it. It was part of a pattern of off-the-books interactions between the Trump campaign and Kislyak. One of Trump’s top surrogates, then-Senator Jeff Sessions, met with Kislyak twice, but told his colleagues during his confirmation hearings for attorney general that he had no contact with Russians during the campaign. Two other campaign aides, Carter Page and J.D. Gordon, spoke to Kislyak following a panel at the Republican National Convention. And Trump’s first national-security adviser, Michael Flynn, was forced to resign after mischaracterizing his conversations with the former ambassador.

The Trump Administration Made Early Attempts to Lift Russia Sanctions

Just days after Trump took office, his administration looked into lifting the sanctions that former President Barack Obama had imposed on Russia over its meddling in the 2016 election. Tom Malinowski, who stepped down in January 2017 as Obama's assistant secretary of state for human rights, told me last June that he and Daniel Fried—then the chief U.S. coordinator for sanctions policy—scrambled to lobby Congress to halt the development of a sanctions-lifting package being considered by the White House after government officials began ringing "alarm bells about possible concessions being made" to Russia. (Malinowski was lobbying unofficially). By that time, the FBI, CIA, and NSA had concluded that the Russians had interfered in the election to derail Hillary Clinton’s candidacy.