President Donald Trump and his inner circle are marking the one-year anniversary of special counsel Robert Mueller’s appointment to with a barely veiled threat: shut down the Russia investigation as soon as possible.

Trump himself frequently rails against Mueller’s inquiry on social media, as he did again on Thursday morning:

But other administration officials are speaking out, too. “Our administration has provided more than a million documents; we’ve fully cooperated in it, and in the interest of the country, I think it’s time to wrap it up,” Vice President Mike Pence told NBC News last week. “I would very respectfully encourage the special counsel and his team to bring their work to completion.”

Rudy Giuliani, a member of Trump’s legal team, put it even more bluntly. “We are going to try as best we can to put the message out there that it has been a year, there has been no evidence presented of collusion or obstruction, and it is about time for them to end the investigation,” he told Bloomberg, adding a thinly veiled threat: “We don’t want to signal our action if this doesn’t work—we are going to hope they listen to us—but obviously we have a Plan B and C.”

Though Mueller was appointed a year ago this Thursday, the investigation into whether the Trump campaign colluded with Russia predates him by nine months. In the summer of 2016, the FBI opened the inquiry under the codename Crossfire Hurricane—a reference to the Rolling Stones song “Jumpin’ Jack Flash”—as a discrete counterintelligence probe known only to a handful of people in federal law enforcement. Much remains unknown about the ongoing investigation, including its size and scope during the period between the presidential election and Trump’s firing of FBI Director James Comey the following May. After Comey’s ouster and Mueller’s appointment as special counsel eight days later, the investigation appeared to intensify as Mueller hired a new, all-star prosecutorial team that’s brought charges against 19 people to date.

Despite those steps, history suggests that Mueller may still take a long time to reach any final conclusions. The paradigmatic example is the Watergate inquiry, led first by special prosecutor Archibald Cox and then by Leon Jaworski after President Richard Nixon ousted Cox in the Saturday Night Massacre. Like Mueller, Cox oversaw an investigation already in progress: The Justice Department appointed Cox on May 18, 1973, almost a year after the initial break-in at the Democratic National Committee’s office in the Watergate complex. A D.C. jury found the burglars guilty four months before Cox took over the probe and inquiries continued into 1976.

In November and December 1986, news outlets uncovered a Reagan administration scheme to sell arms to the Iranian government and then funnel the proceeds to right-wing rebel groups in Nicaragua that were battling the socialist Sandinista government. Lawrence Walsh, the Iran-Contra special prosecutor, spent the next seven years scrutinizing White House officials and the U.S. foreign-policy establishment before filing a final report in 1993.

The following year, a three-judge panel in D.C. appointed Kenneth Starr as independent counsel to investigate a range of alleged scandals in the Clinton White House, including a closely scrutinized real-estate deal in Arkansas known as Whitewater. Starr’s probe eventually morphed into an investigation into whether Clinton lied about his marital affair with White House staffer Monica Lewinsky, culminating in the president’s impeachment in 1998. It wasn’t until 2002 that Starr’s successor, Robert Ray, released his final conclusions on the Whitewater deal and its ancillary scandals.

By comparison, the Russia investigation is still young. “In absolute terms, I don’t think you can say that this investigation as special prosecutions go is overly long,” Paul Ware, who served on the Iran-Contra prosecutorial team, told me. “To my way of thinking, what makes it feel long is the absence of any kind of substantive leak or basis on which people can conclude that there’s not only smoke, but that there’s fire.”

Questions about Mueller’s timeframe can cut both ways. The U.S. will hold its midterm elections in less than six months, increasingly putting the special counsel in a bind. Justice Department policies generally warn federal prosecutors against undertaking major investigative steps near an election to avoid the appearance of influence.

“One would think that common sense dictates going public with some substantive decision very soon—by June at the latest—or not going forward until after the election,” Ware said. “Any responsible prosecutor, including Bob Mueller, would be disinclined to become a factor in the election itself, and you saw what happened when Comey started making comments on two different occasions, and the fear that that’s caused and the potential impact that that had on the election.”

It’s understandable why Trump and his associates want Mueller to wrap up soon. The investigation is a media obsession, hanging a dark cloud over the administration, and the scrutiny of federal prosecutors has put the White House constantly on edge. But the president is no ordinary subject of an investigation. Unlike virtually any other potential defendant in the country, Trump alone can fire the man who’s investigating him. That makes his threats to fire Mueller—which he has privately considering doing at least twice—a unique challenge to the American rule of law. “We’ll see what happens,” Trump said last month. “Many people have said, ‘you should fire him.’ Again, they found nothing and in finding nothing that’s a big statement.”

But it’s clear that Mueller has found some things, given the indictments thus far, and only the special counsel’s office knows whether it has found evidence that Trump colluded with Russia to interfere in the 2016 election. The Senate Intelligence Committee, in a bipartisan statement on Wednesday, confirmed that Russia meddled to help Trump and hurt Hillary Clinton. Later that day, Giuliani claimed to have knowledge that Mueller won’t indict the president even if the investigation uncovers evidence of wrongdoing. (There’s a longstanding legal debate, inside and outside the Justice Department, about whether the Constitution allows a sitting president to be indicted.)

The political damage inflicted by this whole affair is largely of Trump’s own making. The president himself set in motion the events that led to Mueller’s appointment when he abruptly fired Comey last May. Trump quickly undermined the party line for the dismissal by linking it to the Russia investigation, then threatened to release “tapes” of his conversations with the ousted FBI director. That tweet prompted Comey to go public with his now-famous memos that detailed the president’s months-long pressure campaign against him. Had Trump left Comey alone, Mueller likely would have no reason to pursue whether Trump obstructed justice.

Even the president’s staunchest supporters realize the implications of another high-profile dismissal. For the one-year anniversary of Mueller’s appointment, The Washington Post interviewed Trump voters about the Russia investigation. When asked to summarize it so far, the voters gave the party line: that it’s a politicized “witch hunt” aimed at undermining Trump’s presidency. But they also didn’t think Trump should shut down the inquiry. As one woman said, “People would be suspicious.”