But Milley's testimony may also open him up to questions about his last weeks and months serving Trump, highlighting how he has become one of the most politicized senior military leaders of recent times. He is one of several normally apolitical figures dragged into the partisan fray, largely due to extreme pressures imposed on the fabric of US government -- and the barriers that normally exist between politics and the military -- by the former commander in chief.
Milley's own apparent willingness to cooperate with the accounts exposing the fraught final days of the Trump presidency has, meanwhile, opened him to criticism that he is playing his own political games. Milley was already a controversial figure after being forced to apologize for accompanying Trump to a notorious political photo op in Washington in the wake of George Floyd's death at the hands of a Minneapolis police officer in May 2020. The stunt took place in Lafayette Square not long after the area had been violently cleared of demonstrators.
In the hearing on Tuesday, and a second session before the House Armed Services Committee the next day, Milley will come face-to-face with some of his most fervent Republican critics -- some of whom will have every incentive to confront him given Trump's antipathy for the general, whom he blasted as "stupid" at an incendiary rally in Georgia on Saturday night.
Republicans accused Milley of greatest military transgression
Milley heads into the hearing facing charges from Republicans that he went behind Trump's back to assure China that the then-President wouldn't stage an attack on the rising Asian superpower and of subverting civilian control of the military by warping the chain of command. In their new book, "Peril," Washington Post reporters Bob Woodward and Robert Costa report that Milley feared Trump's mental condition had deteriorated seriously in his final days in office and that he called a meeting of top commanders to tell them not to take orders for military action, including with nuclear weapons, without talking to him.
"You never know what a President's trigger point is," Milley told his senior staff, according to the book, which also reported his contacts with top Chinese military officers.
Republicans, especially Sen. Marco Rubio, seized on the reports to accuse Milley of effectively fracturing civilian control of the armed forces by deciding that the military's judgment was more stable than that of the commander in chief. The Florida senator demanded that Biden fire Milley, and accused him of contemplating a "treasonous leak" to the Chinese Communist Party.
According to "Peril," Milley made two calls across the Pacific after becoming concerned that Beijing feared Trump's volatile mood after losing the Oval Office could lead him to lash out militarily.
On a trip to Europe earlier this month, Milley said the contacts were nothing out of the ordinary but pledged to talk about his conduct in the post-election period at the hearing if asked.
"I will go into any level of detail Congress wants to go into," he said.
Sen. Marsha Blackburn of Tennessee, for instance, said Milley, Biden, Austin, Vice President Kamala Harris and Secretary of State Antony Blinken and others should resign or be impeached over the Afghanistan withdrawal. Another pro-Trump GOP committee member, Sen. Josh Hawley of Missouri, who was among the lawmakers who challenged the certification of Biden's election victory, accused Milley of breaking the chain of command.
Fears of a coup
Milley's appearance before the hearing also comes amid a flurry of new disclosures about the tumultuous events leading up to the US Capitol insurrection by a mob incited by the ex-President on January 6. In one, CNN published a memo by a pro-Trump lawyer detailing steps then-Vice President Mike Pence could take to block the certification of Biden's election victory, which was first revealed in "Peril."
He is quoted as telling aides that Trump was the "classic authoritarian leader with nothing to lose" and that the United States could be facing a "Reichstag" moment -- referring to the fire at the German parliament used as a ruse by Adolf Hitler's Nazi Party to cement power in the 1930s.
These are stunning reports, which Milley has yet to fully address in public since they emerged. And again, there must be questions over whether the top uniformed military officer has allowed himself to get too sucked into political tumult.
But at the same time, and as was also the case in the notorious moment in Lafayette Park, no chairman of the Joint Chiefs in the modern era has faced the kinds of extreme circumstances that Milley stared down, a factor that historians are likely to consider when they assess his role.
The idea that a defeated commander in chief might plot a coup -- apparently validated by subsequent revelations -- would have been unthinkable before Trump. And no modern president has torn at the conventions of political and military procedure like Trump.
In that sense, Milley's testimony might also serve a role as a cautionary tale about what might lie ahead if Trump, currently the apparent favorite for the 2024 Republican nomination, were to capture the White House again. Milley is one of a few senior figures, including Republican officials in some battleground states, who stood firm against Trump's multi-front efforts to subvert the will of voters and cling to power.
It is far from clear that Milley did subvert the civilian chain of command -- contacts with Chinese military officers are routine and, in the event, there was no order for politically motivated military action from Trump. But the fact that the most powerful uniformed officer in the United States thought it might be necessary to intervene to stave off a disaster raises a frightening scenario. And it may invite debate about the current system, under which a President has streamlined power to order a nuclear attack within minutes -- a process in which the chairman of the Joint Chiefs is not directly involved.
It also seems unlikely that Trump, if he were to win a second term, would take any chances on naming top military brass who he was not convinced were totally loyal to his cause.