Thursday marks one year since special counsel Robert Mueller was appointed to investigate Russian meddling in the 2016 US election. Mueller took over an investigation that was first opened by since-fired FBI Director James Comey in July 2016, during the campaign.

The far-reaching investigation continues -- witnesses are still being interviewed, and trials are scheduled for later this year. As the proceedings have dragged on, the White House has adopted an increasingly hostile tone toward the investigation, which President Donald Trump has repeatedly called a "witch hunt" and a "hoax."

Here is a breakdown of what we know about one year of the investigation under Mueller, by the numbers:

In one year, Mueller has brought charges against 19 people and three companies, including a former White House adviser, three former Trump campaign aides – including the campaign chairman at the time – a prominent Russian oligarch and a dozen Kremlin-backed trolls. In all, these defendants are facing a combined 75 criminal charges, ranging from alleged conspiracy against the United States, bank fraud and tax violations to lying to FBI investigators and identity fraud.

Five defendants have pleaded guilty, including former national security adviser Michael Flynn and former Trump campaign aide Rick Gates.Both are cooperating with Mueller. Alex van der Zwaan, a Dutch lawyer who pleaded guilty to lying to the special counsel, is currently serving a 30-day prison sentence.

Former campaign chairman Paul Manafort is fighting Mueller's charges in court.

At least 40 people have voluntarily given interviews to Mueller's investigators, according to CNN's latest reporting and other news accounts. At least seven people are known to have testified at a grand jury, though the number is likely much higher because the proceedings are secret.

Earlier this year, Trump's lawyers touted an "unprecedented" level of cooperation with Mueller. They boasted that the White House had handed over 20,000 pages to Mueller and the Trump campaign had produced an additional 1.4 million pages of documents. They also noted that at least 20 White House staffers "voluntarily" gave interviews to Mueller's investigators, including eight people from the White House Counsel's Office.

The President has not yet been interviewed, but negotiations are underway for him to provide testimony. CNN has reported that in at least one meeting, Mueller raised the possibility of a subpoena to compel Trump's testimony. Trump has said he would "love to speak" to Mueller, so long as he is "treated fairly."

Trump changed his tone by the next day, calling the probe a "witch hunt." He's used that phrase 39 times since the Mueller probe began until Thursday - when he used it again in another tweet blasting the investigation.

Mueller has assembled a team of at least 17 lawyers and "dozens" of FBI agents to help with his investigation. Nine of the lawyers donated to Democratic candidates before 2017, according to federal records. Eight of those lawyers gave only to Democrats, while one has donated to Democrats and Republicans before.