 It’s been one year to the day since Robert Mueller was appointed special counsel to investigate "any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump." 
 
 Mueller’s appointment came in the wake of Trump’s decision to fire FBI Director James Comey, who was then heading the investigation. Allegations had also surfaced that Trump had asked Comey to scale back the probe into former National Security Adviser Michael Flynn. Mueller was granted the authority to prosecute any federal crimes he uncovered. 
 
 Mueller served in the Vietnam War as a Marine, receiving a Purple Heart. Following a career in both the public and private sectors, including several years as a federal prosecutor, Mueller served as FBI director from 2001 to 2013. He gave up his position with the law firm WilmerHale to take the special counsel appointment. 
 
 In its first year, the Mueller investigation has remained tight-lipped about its activities, except when it comes to indictments and plea deals. The investigation has obtained five guilty pleas, plus indictments numbering in the double digits. The team has done this while coming under attack by Trump and his allies, who allege partisan bias and decry it as a "disgusting, illegal and unwarranted witch hunt." 
 
 Meanwhile, the investigation’s endgame could involve complicated legal decisions about whether presidents can be subpoenaed or indicted, and whether Trump can fire Mueller or use pardons to stymie the probe. 
 
 Who’s on Mueller’s team? 
 
 The Special Counsel’s office had made public the identities of 17 attorney staff members, spurring Trump to criticize the investigators are largely "hardened Democrats." 
 
 Through public records, we were able to independently confirm that at least 12 people on Mueller’s staff are registered Democrats. Two others are registered to vote but have not chosen a party affiliation. We were unable to independently confirm the status of two other staff members. 
 
 Mueller, though, is registered as a Republican in the District of Columbia and was appointed to offices by Republican presidents Ronald Reagan, George H.W. Bush and George W. Bush, as well as by Democrats Bill Clinton and Barack Obama. 
 
 In addition, Mueller was appointed by Rosenstein, who was nominated for deputy attorney general by Trump himself, and who previously was appointed as a U.S. Attorney by George W. Bush (and later kept on by Obama). 
 
 It’s worth noting that other FBI or Justice Department personnel are assisting the investigation in certain capacities, but the names of investigative and office support personnel have not been made public. 
 
 Mueller was prevented from considering political affiliation when putting together his team by both Justice Department policy and the Civil Service Reform Act. Moreover, the career attorneys on the Mueller team are bound by professional codes to pursue justice and rise above partisanship. 
 
 What has the investigation produced so far? 
 
 Within a month of his appointment, Mueller began looking into the question of whether Trump obstructed justice. 
 
 On Oct. 30, 2017, Paul Manafort and his business partner Rick Gates — two former senior officials with the Trump campaign — were indicted on 12 counts related to their political consulting business, including money laundering. Also on that day, George Papadopoulos, a former Trump campaign aide, pled guilty to making false statements to the FBI. 
 
 On Dec. 1, 2017, Flynn pled guilty to making false statements to the FBI about conversations he’d had with then-Russian ambassador Sergey Kislyak. 
 
 On Feb. 16, 2018, Mueller indicted 13 Russian nationals and three Russian entities on charges related to the 2016 election. 
 
 Days later, Dutch lawyer Alex van der Zwaan pled guilty for lying to the FBI about his dealings with Gates and another unnamed person. He was later sentenced to 30 days in prison. 
 
 On Feb. 22, Mueller upped the ante against Manafort and Gates with 32 new financial charges. Within days, Gates pled guilty to conspiracy and lying to the FBI. Manafort, however, has continued to fight his charges. 
 
 Beyond these official acts, the Mueller investigation has publicly announced little about what it is doing, and leaks from its own ranks have been scarce to nonexistent. So its activities remain largely hidden. 
 
 Can Mueller subpoena Trump? 
 
 Most legal experts told PolitiFact that being president doesn’t offer blanket protection against a subpoena, as Trump lawyer Rudy Giuliani has claimed. But there are enough gaps in the legal precedent that Trump’s team could raise legal challenges that the courts would have to take seriously. 
 
 In a case involving President Bill Clinton, the U.S. Supreme Court ruled that a civil suit could go forward against a sitting president, rather than having to wait until their term was over. Given that the court green-lighted a presidential interview in a civil suit such as this one, it might be even more likely to do so in a criminal investigation, experts said. But the reality is that no one knows how the high court would rule in a criminal case related to Mueller’s investigation. 
 
 Meanwhile, in the Watergate-related case United States vs. Nixon, special prosecutor Leon Jaworski wanted tapes of President Richard Nixon talking to his aides. Nixon, citing executive privilege, refused to hand them over. But the high court unanimously sided with the prosecution. 
 
 This decision suggests that presidents are not exempt from subpoenas in a criminal investigation. That said, it may depend on the nature of the subpoena. The court today could decide that a subpoena for in-person questioning -- rather than documents or tapes -- could be overly broad, or that some potential subpoena requests fall too far outside the scope of Mueller’s investigation. 
 
 Can Mueller indict Trump? 
 
 Officially, there has never been a binding judicial opinion on this question. 
 
 "It is unresolved," said Erwin Chemerinsky, dean of the law school at the University of California-Irvine. "The Watergate grand jury in 1974 named Richard Nixon an ‘unindicted co-conspirator’ because they did not know if they could indict a sitting president." 
 
 That said, there is a widespread assumption among legal experts that courts would rule against the idea of prosecuting a sitting president. 
 
 This is primarily due to a pair of opinions by the Office of Legal Counsel, the closely watched office within the Justice Department that advises presidential administrations on the legality of taking certain positions or actions. 
 
 The office looked at this question in 1973 and 2000, concluded on both occasions that a president could not be criminally prosecuted. Criminal prosecution, the office determined, would undermine the executive branch’s ability to perform its functions. Ultimately, "only the House of Representatives has the authority to bring charges of criminal misconduct through the constitutionally sanctioned process of impeachment," the office wrote in 2000. 
 
 Can Trump fire Mueller? 
 
 Over the course of the year, Trump has mulled, privately and publicly, whether he should remove Mueller. 
 
 Mueller’s potential removal falls into a legal gray area that involves Justice Department regulations, congressional statutes and constitutional law. 
 
 Under Justice Department regulations, only the attorney general can fire Mueller. In this instance, Rosenstein, who’s acting as attorney general in place of Attorney General Jeff Sessions for this purpose, would have that authority. (Sessions recused himself from the investigation.) 
 
 The regulations also state that in order to fire Mueller, there has to be a good reason — specifically "misconduct, dereliction of duty, incapacity, conflict of interest, or for other good cause, including violation of departmental policies." 
 
 Under this scenario, Trump could order Rosenstein to fire Mueller, but Rosenstein could refuse if he believed that there had been no misconduct by Mueller. 
 
 Alternately, the president could fire Rosenstein, and then continue firing Justice Department brass until someone was willing to fire Mueller. But the official who ultimately carried it out could face enormous public blowback. 
 
 A third possibility is that Trump could seek to rescind the Justice Department regulations. However, this would require a lengthy process that would allow Mueller to continue operating in the meantime. 
 
 What if a court decided that Mueller’s appointment — and firing — was governed by congressional statute rather than the Justice Department rules? That would allow Trump to fire Mueller directly, since the congressional statute contains no requirement for misconduct before a firing. 
 
 However a firing was carried out, Mueller would have standing to challenge it in court. 
 
 A more promising course for Trump than firing Mueller might be convincing Sessions to narrow the scope of his recusal. If Sessions agreed to do that, he could curb the scope of Muller’s probe. 
 
 Could Trump use pardons to get around Mueller? 
 
 As early as July 2017, news reports suggested that the White House and its legal advisers were weighing whether and how to use the president’s power. 
 
 Can the president pardon himself? Even legal experts who are skeptical acknowledge that no one knows for sure. 
 
 The Constitution doesn’t explicitly prohibit a self-pardon, except in the case of impeachment. However, experts said there are several more circumstantial arguments that, collectively, make a strong case that a self-pardon would be impermissible. 
 
 The Constitution uses the word "grant," which ordinarily means giving to someone else, said Harold H. Bruff, an emeritus University of Colorado law professor. Going back to its English monarchical origins, a pardon has long been conceived as an act of mercy. Neither of these suggest something that can be done to oneself. 
 
 In addition, Bruff said that when the Constitution was being written, "a background value everywhere in the air was that no one should be a judge in their own cause." This notion, sometimes referred to in Latin as "nemo judex in causa sua," is a longstanding common-law principle, he said. 
 
 It’s worth noting a downside of a president pardoning themself: It’s a tacit acknowledgement that they had committed a crime, which could supercharge impeachment efforts. 
 
 Pardoning presidential associates could be more effective, but that would not be a cure-all for Trump, either. 
 
 "A pardon would not end an investigation into any one person as the investigation is about the Russian interference with the election," Robenalt said. "The fact that someone may be pardoned or dead matters not to an investigator who is trying to connect dots." 
 
 To truly shut down the probe using pardon power, a president would either have to separately pardon a multitude of individuals by name — a rolling game of "Whac-a-Mole," as Bruff put it — or else issue a blanket amnesty. While such blanket amnesties have been implemented before, none have been enacted to protect a presidency. 
 
 CORRECTION, May 17, 2018, 12:00 noon: This version corrects the number of guilty pleas obtained by Mueller. It is five, not four.
– Thursday is the one-year anniversary of the start of Robert Mueller's investigation, and President Trump is among those marking the occasion. His tweet, however, drips with sarcasm. "Congratulations America, we are now into the second year of the greatest Witch Hunt in American History ... and there is still No Collusion and No Obstruction," he writes. "The only Collusion was that done by Democrats who were unable to win an Election despite the spending of far more money!" In another tweet, he calls the investigation "disgusting, illegal and unwarranted" and said his administration has nonetheless had "the most successful" first 17 months of any White House, "by far!" Related coverage: The basics: Mueller was appointed special counsel to investigate "any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump," explains PolitiFact. Mueller quickly expanded his investigation into whether Trump obstructed justice, notably by firing FBI chief James Comey. The piece hits other nuts and bolts of the investigation.