Attorney General Merrick B. Garland is intent on avoiding even the smallest of mistakes that could taint the ongoing investigation, give Mr. Trump’s defenders grounds to claim the investigation was motivated by hostility, or undo his effort to restore the ministry’s reputation after the political war of the Trump years. Mr. Garland never seriously considered focusing on Mr. Trump from the start, as investigators had earlier done with Mr. Trump and Mrs. Clinton during their email probe, people close to him say. As a result, his investigators took a more methodical approach, carefully climbing the personnel chain behind the 2020 plan to name fake Trump voter tesserae in battleground states won by Joseph R. Biden Jr. As prosecutors dig deeper into Mr. Trump’s trail, the former president and his allies in Congress will almost certainly accuse the Justice Department and the FBI of a politically motivated witch hunt. The template for these attacks, as Mr. Garland and FBI Director Christopher Wray are well aware, was “Crossfire Hurricane,” the investigation into the Trump campaign’s ties to Russia, which Mr. Trump is continuing to dismiss as partisan farce. The mistakes and decisions of that period, in part, led to increased levels of oversight, including a major policy change at the Justice Department. If a decision were made to open a criminal investigation into Mr. Trump after he announced his intention to run in 2024, as he has proposed doing, department leaders would have to sign off on any investigation under an internal rule enacted by Attorney General William P .Barr and seconded by Mr. Garland. “Attorney General Garland and those investigating high-level efforts to overturn the results of the 2020 election know all too well how any mistake, whether by the FBI or prosecutors, will be amplified and used for political purposes,” said Mary B. McCord. , a top Justice Department official during the Obama administration. “I expect there are additional layers of review and scrutiny for every step of the investigation.”

Key revelations from the January 6 hearings

Card 1 of 9 Suing Trump. The House committee investigating the January 6 attack presents a comprehensive account of President Donald J. Trump to overturn the 2020 election. Here are the main themes that have emerged so far from eight public hearings: Mr. Wray appears to be proceeding with the same level of caution, hoping to shield the bureau from future attacks by ensuring its agents operate by the book and keeping Justice Department leadership informed. That means following the FBI’s strict rules and “not just doing the right thing, but doing it the right way,” Mr. Wray has often said. It also means that Mr. Wray would not go it alone, as his predecessor, James B. Comey, famously did. The typically aggressive bureau, which used every investigative tool in its arsenal during the Russia probe, didn’t even open a case targeting voter fraud until early fall 2021, months after details of the sprawling scheme became known. two former federal police officials said. In 2015, amid the outcry over Mrs. Clinton’s use of a personal email account, senior FBI officials — without consulting top department officials, including Mr. Comey — opened a criminal investigation into whether she had mishandled classified information . In May 2017, the FBI opened its own investigation into obstruction of Mr. Trump, trapping the leadership of the Justice Department and igniting a political firestorm. The decision also fueled suspicions by Mr. Trump and his supporters that the so-called deep state was out to undermine his presidency. In the wake of Mr. Trump’s election victory, Mrs. Clinton and her supporters blamed Mr. Comey, arguing that his unusual public statements about the status of her email investigation had inadvertently swayed the outcome of the race. The new president would soon find fault with the manager as well. Mr. Trump’s willingness to attack the Justice Department was on the minds of department and bureau officials as they sought to respond to the Jan. 6 attack and other efforts to reverse Mr. Trump’s loss, current and former officials said. The lawyers who ran the department at the time, including the deputy attorney general, Jeffrey A. Rosen, and the deputy attorney general, Richard P. Donoghue, managed to prevent Mr. Trump from usurping their authority so he could stay in office illegally. They were under no illusions about his willingness to undermine any investigation. They also knew that many of their decisions would eventually become public. That reinforced their tendency not to make bold moves before President Biden’s team took over, in case their actions were publicly scrutinized in oversight hearings — especially if Republicans regained control of Congress. On the afternoon the rioters stormed the Capitol, Mr. Garland was finishing a speech on the rule of law. He watched on television as Congress turned into a crime scene that he would soon have to investigate. Everyone who witnessed the attack “understands, if they didn’t understand before, the rule of law is not just the lawyer’s turn,” Mr Garland said at a ceremony the next day. “Failure to make it clear in word and deed that our law is not the instrument of partisan purpose” would endanger the country, he added. Mr. Garland has been examining the Justice Department’s role in democracy since the 1970s, when he worked for Attorney General Benjamin R. Civiletti to help codify changes that addressed presidential abuses of power since the Watergate era. In late March, when Mr. Garland took over the department, he embraced the bottom-up tactics already being used by the acting US attorney in Washington appointed by Trump: round up and arrest the perpetrators, and then maybe the their communications and interviews to yield information that would lead them to more powerful targets. That approach — epitomized by the mantra of investigating “crimes, not people” — has sometimes led to tensions between top officials and the federal prosecutors in Washington who conduct the investigation on a daily basis. From the start, Mr. Garland and his top deputy, Lisa O. Monaco — a former senior FBI official and a detail-oriented former federal prosecutor — set the bar high. But they did not stop prosecutors from pursuing avenues they believed were supported by evidence: Ms. Monaco urged prosecutors to devote additional resources to investigating terrorist financing and possible ties to foreign governments, according to a former department official. The department did not appear to immediately take advantage of public revelations in the fall of 2021 that a top Trump lawyer, John Eastman, had promoted the voter fraud scheme. But gradually, mostly hidden from public view, they began to pursue that lead and others that eventually led them to question Mr. Trump’s involvement more directly. At the time, Christopher R. Kavanaugh, who had gained extensive experience in domestic terrorism as a prosecutor in Charlottesville, Va., after the deadly far-right rally there in 2017, was assigned to manage the sprawling Jan. 6 investigation. The investigation involved nearly every state in the country and involved hundreds of suspects. When Mr. Cavanaugh left the role after hundreds of arrests in early October to become U.S. attorney in Charlottesville, he was replaced by Thomas P. Windom, an aggressive but little-known federal prosecutor from Maryland who had also handled domestic terrorism high profile. cases. Mr. Windom expanded the voter survey, according to people with knowledge of the situation. He also closely followed a separate investigation by the department’s inspector general into Jeffrey Clark, a former Justice Department official who was central to Mr. Trump’s failed effort in late 2020 to strong-arm the nation’s top attorneys to support the allegations. of. electoral fraud. Both of those probes had already gained momentum as the House committee hearing on Jan. 6 ramped up its much more public inquiry — one designed to pressure Mr. Garland to move faster to go after Mr. Trump. By April, prosecutors had recovered emails from senior officials in the Trump White House. In June, the inspector general obtained warrants for electronic devices belonging to Mr. Clark, Mr. Eastman and Ken Klukowski, another former Justice Department official. A lawyer for Mr. Klukowski said his client is cooperating fully with the Justice Department and will continue to do so. And on Wednesday, following the news that two top aides to former Vice President Mike Pence appeared before a grand committee, Mr. Windom filed notice in the US District Court in New Mexico. It revealed that a federal agent had obtained a second search warrant earlier this month for Mr. Eastman’s phone — the first time Mr. Windom’s name appeared in a public filing filed in a Trump-related case. After those search warrants, the Justice Department created a so-called filter team to deal with any privileged information that came from those warrants, according to the filing. Previously, it was only known that the department’s inspector general had obtained a search warrant for Mr. Eastman for a closer internal investigation of the department that had begun after the Jan. 6 riot. In his public statements, Mr. Garland has demonstrated an awareness of the extraordinary dangers that…