That’s an interesting question I was also very curious about. This is what I found:
We can only guess what Mueller is doing based on who he has hired so far—top expert lawyers (16 and counting) on criminal fraud, foreign bribery, cybersecurity, etc.
The top mandate is to investigate Russia’s impact on the 2016 presidential election; then whether members of Trump’s campaign collaborated with Russia in any way; and whether Trump obstructed justice when firing Comey. Additionally, Mueller can pursue any leads on suspected crimes that may arise directly from these areas of focus during the fact-finding process.
Mueller has likely already looked at information in the Treasury Department’s Financial Crimes Enforcement Network (FinCEN) database, possibly in relation to Trump’s businesses, casinos, and real estate deals (or if not related to Trump himself yet, certainly for any number of shady people like Paul Manafort, Felix Sater, etc.)
As of a few days ago, news reports revealed Mueller also enlisted the help of the IRS Criminal Investigations Unit that specializes in financial crimes like tax evasion and money laundering.
I don’t think there are any fixed time limits for the investigation, per se. The parameters and boundaries of Mueller’s investigation must be approved by the Attorney General (in this case, Deputy AG).
This is Rosenstein’s letter (PDF) appointing Mueller as Special Counsel. It seems Mueller has been given a lot of leeway.
That being said, firing Mueller (or potentially any Deputy Attorney General who refuses to do his bidding) has crossed Trump’s mind before. Trump might be the most proximal threat to the investigation’s time table. Whether or not Trump would actually fire him, Mueller has likely prioritized investigative matters keeping that possibility in mind. Indeed, last month several members of the Senate Judiciary Committee with similar concerns introduced bills to try to prevent firing of a Special Counsel without judicial review.
Another possibility that could cut the investigation short is if some Republican lawmakers try to curb it. Rep DeSantis (R-FL) has recently floated the idea of restricting the investigation’s duration to 180 more days and isolating its scope to events after June 2015 when Trump announced his run for president.
Restricting funds seems to be a common way lawmakers try to kill projects, agencies, committees, investigations, and other agendas they don’t like.
How big of a staff will Mueller get, and who decides that?
The federal code does not specify how large a staff the special counsel is afforded. It says only that a special counsel “shall be provided all appropriate resources by the Department of Justice.” The code notes that special counsels may request the assignment of Justice Department staff to assist them, and that such employees will be supervised by the special counsel. Special counsels also may request additional staff from outside the Justice Department, and “[a]ll personnel in the [Justice] Department shall cooperate to the fullest extent possible with the Special Counsel.” The special counsel’s proposed budget is subject to approval by the acting attorney general. The length of the investigation is not mandated, but federal code requires the special counsel to make a budget request each fiscal year, at which point the acting attorney general “shall determine whether the investigation should continue and, if so, establish the budget for the next year.”
Per CBS News, funding for Mueller’s team comes from a permanent Treasury Department account with indefinite appropriations (subject to DOJ oversight):
The money to fund the investigation will come out of the government’s “permanent indefinite appropriation” fund which is allocated specifically to pay for all necessary expenses of investigations and prosecutions by independent counsels.
Mueller will submit his budget to the Justice Department’s Assistant Attorney General for Administration Lee Lofthus. Lofthus says there is no real limit, and Mueller will get any funds he deems necessary, subject to the approval of the deputy attorney general.
Some pundits have speculated Mueller is still in the somewhat early stages of his investigation, about 20-25% complete.
Robert S. Mueller III was appointed as Special Counsel on May 17, 2017. Up through today (September 3, 2017), his investigation has lasted 110 days and counting.