Jonathan Turley, testifying before the House Judiciary Committee on Wednesday, outlined one of the reasons he opposes an impeachment of President Trump at this moment.

“Fast is not good for impeachment,” the George Washington University law professor said. “Narrow, fast impeachments have failed. Just ask Johnson.” Turley was referring to President Andrew Johnson, who was impeached by the House in 1868. More on him in a bit.

If Turley had meant to caution Congress to spend more time digging into the allegations against Trump and to encourage the House not to move forward too quickly, his words were not heeded by House Speaker Nancy Pelosi (D-Calif.).

“Sadly, but with confidence and humility, with allegiance to our founders and our heart full of love for America, today I am asking our chairmen to proceed with articles of impeachment,” Pelosi said Thursday morning. “I commend our committee chairs and our members for their somber approach to actions which I wish the president had not made necessary.”

Turley’s point broadly wasn’t really about expediency but about his perception that the evidence warranting impeachment didn’t yet exist. (Three other witnesses who are legal scholars disagreed in stark terms.) It’s nonetheless important to note that “fast impeachment” is an odd term to deploy in the context of presidential impeachments simply because there are so few examples against which speed can be compared.

There have been four robust efforts to impeach presidents, targeting Trump, Johnson, Richard Nixon and Bill Clinton. Timelines get a little hazy, since some components of impeachment efforts — like the drafting of articles of impeachment — happen over extended periods. From the first formal vote to begin impeachment until the initial House vote (or, in the case of Nixon, his resignation), though, those efforts unfolded like this.

Johnson’s was, in fact, fast. Shortly after the House voted to begin the process, articles of impeachment were drafted, according to the Senate historian. In the cases of Nixon, Clinton and Trump, articles of impeachment began to be drafted after 170, 64 and 35 days, respectively (assuming that the House gets to work on Thursday). If the House votes on the articles against Trump on Christmas (apparently one target for the Democrats), the Trump process will have taken 55 days. In contrast, Nixon’s took 183 days and Clinton’s 72.

From the first House vote to the impeachment vote, Johnson’s impeachment took a week. Contrary to Turley’s claims, though, it wasn’t particularly unsuccessful: Johnson, like Clinton, was impeached by the House.

That wasn’t the end of the process, of course. After the House votes, Johnson and Clinton were tried by the Senate, a process that began almost immediately for Johnson and after about a month for Clinton (because of the 1998 holiday season). Clinton was cleared by the Senate after about a month; Johnson in multiple votes two months down the line.

It’s not clear how long after a House vote to impeach Trump that a Senate trial might begin. It’s important to note that, as we reported in September, there’s a dramatic shift in power once that happens, moving from the Democratic-controlled House to the Republican-controlled Senate. Senate Majority Leader Mitch McConnell (R-Ky.) has enormous power to affect how the trial unfolds and how long it takes.

It’s for that reason that many Democrats share Turley’s concern about moving too quickly. To date, the impeachment push has been driven by Democrats, allowing them to call witnesses and focus on testimony as desired. Democrats have been able to define the boundaries of the effort, as well, constraining it to issues related to Ukraine, to the frustration of a vocal part of the party’s base.

What the timelines above obscure, of course, is that impeachment doesn’t begin with a formal House vote. Nixon’s path toward possible impeachment began nearly 600 days before the actual vote to formally begin the process: the break-in at the Watergate Hotel in Washington. An informal process itself began several months before the formal vote in Nixon’s case, just as the House had been conducting interviews related to the formal Trump impeachment inquiry for a month before the full House voted to move forward.

The precipitating event for Trump’s impeachment, that July 25 call with Ukrainian President Volodymyr Zelensky, occurred about 100 days before the formal inquiry began. (There are other things under consideration, of course, just as there were important other factors and actions included in Nixon’s.) The deposition in which Clinton lied under oath came more than 260 days before his formal impeachment got underway.

Johnson’s impeachment began almost immediately after he fired Secretary of War Edwin Stanton, a function of an ongoing dispute between Johnson and Congress over his Cabinet appointments.

Is Trump’s impeachment moving particularly quickly? Not compared with Johnson’s, and that one turned out nearly exactly as Clinton’s did. Tack on a Senate trial of unknown duration and it’s not clear how the Trump impeachment will compare.

But, then, duration isn’t a particularly useful metric here. Democrats might uncover additional evidence if they went more slowly on impeachment; they might not. They might have better luck persuading the public about the merits of impeachment if they spent more time digging into other aspects of Trump’s presidency, but so far, there’s little evidence that much of anything is moving public opinion. Duration serves less as a measure of efficacy than of how one feels about how the inquiry is going.

The odds, after all, are that this impeachment will end the same way two of the other three did: impeachment of Trump by the House and acquittal in the Senate that keeps him in office.