With special counsel Robert Mueller’s decision to charge President Trump’s former campaign chairman, Paul Manafort, and Rick Gates, who worked with Manafort, we have entered a new phase of the controversy over whether Trump or members of his 2016 campaign team improperly colluded with Russian officials.

Trump associates now understand that they could face criminal charges. And the president and his White House advisers must contend with two indictments, including one of Trump’s one-time campaign chairman, and the potential for further charges to be brought against people they are close to. Also, there is no indication that Mueller has cleared the president himself of involvement in the possible collusion — or obstruction of justice to cover up any collusion — so Trump remains to some extent under investigation.

So the Mueller probe is even more serious — both as a political story and a legal one — than it was a day ago. Obviously, the most important figures in this drama are Mueller and the president, who in theory could force the dismissal of the special counsel or pardon everyone suspected of illegal activity. But aside from those two, here are some key players, legal and political, whose reactions to the indictments you should watch closely. I have organized them starting with the most important.

Rod Rosenstein

Remember, Rosenstein, the deputy attorney general, alone appointed Mueller. Attorney General Jeff Sessions recused himself from the Russia investigation. Trump was not involved in the decision and has said he was irritated by Mueller’s appointment. And some of the president’s allies are suggesting that Mueller should resign, arguing that the special counsel has a conflict of interest because of his long-standing relationship with James Comey, whom Trump fired as FBI director. (Mueller is believed to be investigating whether Comey’s firing and other actions by Trump constitute obstruction of justice.)

The clearest route to removing Mueller would be for Rosenstein to fire him, potentially after getting such a request from the president. According to Department of Justice regulations, special counsels can be removed only by the attorney general. With Sessions’s recusal, Rosenstein is the acting attorney general in the Russia investigation.

Rosenstein, testifying at a Senate hearing in June, indicated that he was very unlikely to fire Mueller for any reason. So another route for Trump would be to fire Rosenstein and then whoever is designated to replace Rosenstein in overseeing the Russia investigation (and accepts that role) would then fire Mueller. (This would of course generate comparisons to Richard Nixon’s “Saturday Night Massacre,” in which two top DOJ officials resigned before a third, at Nixon’s insistence, fired the special prosecutor who was investigating the Watergate scandal.)

A third route would be for Trump to order the relevant regulations repealed or just ignore them and announce that he is dismissing Mueller, no matter what Rosenstein thinks.

I don’t expect Trump to attempt to fire Mueller after these indictments. That’s just an informed hunch, but it also means I don’t expect to hear anything from Rosenstein. His silence would be an important sign that Mueller’s investigation is continuing.

Mitch McConnell and Paul Ryan

Trump will likely remain president as long as the House does not vote for impeachment and the Senate does not vote for removal. So the House speaker and Senate majority leader hold Trump’s fate as president in their hands.

We are very far from any real consideration of Trump’s removal. Trump was not charged with anything by Mueller, and he may never be. So at this stage, Ryan’s and McConnell’s reactions will be important in the context of Mueller continuing his investigation. If the two top congressional leaders signal they are upset about Mueller’s work or view it as improper, that could embolden Trump to try to set in motion a process to dismiss the special prosecutor. If McConnell and Ryan either defend Mueller or signal that the investigation should continue, or both, that will raise the political costs of the president trying to end the Mueller probe.

And even short of Mueller’s dismissal, Ryan’s and McConnell’s stances toward the Russia investigation could have significant political effect. Trump and some Republicans have pushed the narrative that the Mueller investigation is purely partisan. That strategy largely worked for then-President Bill Clinton in the late 1990s when he was being investigated by independent counsel Ken Starr. McConnell and Ryan, though, have expressed confidence in Mueller, making it harder for his investigation to be cast as just politics.

Richard Burr

The North Carolina Republican senator is leading the Senate Intelligence Committee probe into Russian interference in the 2016 election. That committee’s investigation has become Congress’ only serious, bipartisan effort to investigate Russian activities and the conduct of Trump and his allies during the campaign. Some of these Republican-led committees have shifted to investigations of allegations about Hillary Clinton instead of Trump. Other committees have seen their investigations break down because of tensions between Democrats and Republicans. But Burr and the committee’s top Democrat, Virginia Sen. Mark Warner, have seemed to work well together.

Burr is the Republican on Capitol Hill with perhaps of biggest combination of 1) knowledge about the various issues Mueller is investigating; and 2) unwillingness to defend Trump at all costs. (Burr was complimentary of Comey when the deposed FBI director came to Capitol Hill and gave testimony that was very unflattering of Trump.)

Mike Conaway, Bob Goodlatte, Trey Gowdy, Chuck Grassley, Devin Nunes and Thomas Rooney

Conaway, Gowdy, Nunes and Rooney are leading the House Intelligence Committee investigation around Russia. (Nunes is the official chairman of that committee, but he has recused himself from parts of its work on the Russia issue after being criticized for sharing too much information about it with White House officials.) Goodlatte runs the House Judiciary Committee; Grassley the Senate one.

Much of the attention of these six politicians is now on Clinton. They are variously looking at whether the FBI’s probe into Clinton’s use of email as secretary of state was done properly and whether there were any funny dealings in the purchase by a Russian agency of a firm heavily involved in the U.S. uranium extraction business. The purchase happened while Clinton was secretary of state, and figures connected in the past to the company had been donors to the Clinton Foundation. There is no evidence that Clinton was informed of the deal.

These men are now the Republican Party’s leading figures on issues around Trump and Russia. If they come out against Mueller, that could also give momentum to a Trump push for dismissal of the special counsel.

The anti-Trump wing of the GOP, in and out of the Senate

Bob Corker, Jeff Flake and John McCain have been increasingly vocal in criticizing Trump, likely partly because none of them is expected to run for office again and face pro-Trump GOP primary voters. Along with Flake and McCain, 10 other Senate Republicans did not endorse Trump in 2016, and many of those members — such as Maine’s Susan Collins and Nebraska’s Ben Sasse — have also been strong critics of the president. I would expect these members, along with anti-Trump figures outside of the Senate, such as conservative writer Bill Kristol, to largely defend Mueller and suggest the indictments raise “serious questions” that need to be explored.

If this wing of the GOP defends the investigation, as expected, that will buttress Mueller in continuing his probe.

It’s also worth watching if the indictments of Gates and Manafort lead this group, particularly Corker, Flake and McCain, to take more direct action in challenging Trump. They have been criticized by liberals for giving strong anti-Trump speeches but not doing much to actually limit the president. Susan Hennessy and Benjamin Wittes, who run the legal blog Lawfare, have said that this trio should pledge to block any Trump nominees for U.S. attorney positions who have met with the president. Hennessy and Wittes said this stance would prevent Trump from choosing who gets the appointments based on how likely he thinks they are to prosecute him or his allies based on their interviews with him.

In short, the anti-Trump wing of the GOP could get a lot more anti-Trump.

The pro-Mueller GOP senators

Lindsey Graham of South Carolina was one of the 12 senators who did not endorse Trump in 2016. But he and North Carolina Republican Thom Tillis are worth watching for another reason: Both have written bills that would attempt to limit Trump’s ability to dismiss Mueller.

Neither bill has moved very much in Congress. But I would expect these members to defend Mueller’s investigation and suggest it should continue. It would be telling if they did not.

The rest of the Republicans in Congress

I expect the rest of the Republicans in Congress to either criticize Mueller and suggest his investigation should wind down soon (think more pro-Trump Republicans like Tennessee Rep. Marsha Blackburn) or to not really say anything about the probe. What would be significant is if some mass of members (say 150 Republicans in House) were to attack Mueller’s investigation and call for its end.

The Democrats

The Democrats just generally don’t have much influence here. What’s worth watching in their reaction — both of members of Congress and those running for seats held by Republicans — is the “i” word. In the time between now and the 2018 midterm elections, does supporting a push for impeachment become a litmus test in the party, with party activists demanding any candidate that they support be committed to trying to remove Trump from office?

It’s still far from clear where the Mueller investigation will take Trump and the country, but keeping an eye on these individuals could give some early clues. In terms of the investigation itself: Will Trump try to oust Mueller? How much support he feels he has for such a move within the GOP might, in part, determine if he tries. On the political side: To what extent do voters view Mueller’s investigation through a partisan lens? The more elected officials treat the probe as partisan, the more the politics of it are likely to play out along partisan lines. Of course, what Mueller turns up will have a say in all this as well.