Earlier this week, Deputy Attorney General Rod Rosenstein named former FBI director Robert Mueller as special counsel to oversee the Justice Department’s ongoing investigation into the Trump campaign’s potential ties to Russia. The history of special counsels is long, fraught and entangled with some of the country’s most infamous political scandals. So FiveThirtyEight turned to an academic expert in the history of — what else? — political scandals for some perspective on what Mueller’s appointment means for the coming weeks and months. Brandon Rottinghaus, a political scientist at the University of Houston, cautioned that while the appointment of a special counsel is indeed a turning point in any investigation, the path forward (including to impeachment) is far from clear. History shows that these investigations can take years and often prove inconclusive.

This interview has been edited for clarity and length.

Clare Malone: You’ve said before that investigations into big fish in the government — like the president — can often end inconclusively. Why is that?

Brandon Rottinghaus: Number one, the president is insulated politically so that it’s hard to get the president’s staff and counsels to turn on the president. There’s an obvious need for the White House to keep the president less connected to the scandal. In this case, the president seems to be doing a lot to put [his] face on it. Other scandals aren’t like this — you have to take a little bit to get to the president’s role.

Number two, presidents are often insulated legally; they have the ability to do a lot of things that staff or Cabinet members aren’t able to do. [Editor’s note: Presidents can, for example, choose to disclose classified information as they see fit.]

The third thing is that independent counsels, special counsels and any other investigatory bodies are reluctant to challenge the president in a way that might lead to impeachment for fear that it looks like a non-democratic outcome to the legal process. Although obviously these things run into partisanship very quickly, people are less willing to remove a president unless the crisis is severe and the implications are egregious.

Malone: So you’re saying Robert Mueller might be wary of being too explicit about the degree of potential wrongdoing?

Rottinghaus: Yeah, the reason that special counsels proceed cautiously is that they’re worried that to push too far too quickly would jeopardize public confidence in the investigation and would potentially disrupt the democratic balance that is imbued in the Constitution. That’s not to say that they’ll pull their punches, but to go so far as to claim presidents have broken the law in some way — that’s something that independent counsels tend to be very circumspect about. If Congress is looking for clear guidelines from the special counsel, it might not be forthcoming.

Malone: How long can the public expect to wait before the special counsel presents his findings?

Rottinghaus: I would say that, on average, your standard investigation, even of a person who’s a Cabinet member or staff member, is probably between two and three years. For a president in particular, it tends to be longer because the amount of care to be taken is greater.

Malone: That’s a long time for the public to live with the story. If we’re looking back at precedent, how do these investigations color the view of the presidency — can it be both good and bad? A boost for the base’s partisanship?

Rottinghaus: I think in the short term there is a rallying around the flag for presidents. There will be a partisan bump for the president, but that is dissipated over the long term as two things happen. Number one, any positive stories you could have are outweighed by negative stories that come out. And number two, these kind of events often lead to legislative paralysis, and if you’re not producing legislation, the public tends to take it out on the incumbent party, especially the president. So it’s a kind of double whammy for presidents looking to keep those approval ratings above water.

Malone: People are asking a lot about whether or not Republicans will abandon Trump — what should the public be watching for in terms of Republican Party leaders signaling their confidence in the president?

Rottinghaus: I would say the first sign of difficulty will be silence as opposed to a vocal defense of the president. I think, though, that there will be a core partisan support for the president no matter what. This goes back to even the days of Nixon and Watergate. Looking at some of the internal polling that was taking place during that period, the White House had supporters right up until the very minute Nixon left office.

I would look at a couple key sets of players. Number one, the Republican leadership — are they willing to go to bat for you publicly and do the Sunday morning talk shows? Tweet about the things that are going well as opposed to going badly? Number two, you want to look at people on the Judiciary Committee or people who are eventually on a select committee, if it comes to that. Those are the people who have specific obligations to investigate and also the power to be able to subpoena you and you records and your staff and your staff’s records. The other organization that tends to get a lot of pressure in these moments are the party committees. When the Republican party stops trying to defend the president, when it begins to try to move on to other things, then I think you’ll get a flavor of how that’s starting to slip away from the president’s grip.

Malone: Anything else for people to keep in mind as they watch this?

Rottinghaus: Presidents are highly stable when it comes to surviving these kinds of things. Though we are in uncharted waters, which it makes predictions hard to be very certain about.