President Donald Trump met with top military officials and gave his approval to activate the D.C. National Guard three days before he encouraged a mob of angry protesters to take their grievances to the U.S. Capitol.

A Pentagon memo released Friday offers these insights, as well as the first detailed timeline of the bungled law enforcement response to Wednesday's insurrection.

The timeline shows that the planning started at least as far back as Dec. 31 and included discussion with select Cabinet members of the potential need for Pentagon reinforcements.

But it also leaves many questions unanswered, including why the U.S. Capitol Police declined repeated offers of assistance from military officials and the full extent of how much Trump knew about the security planning or was involved in decision-making.

The memo, first reported on by NBC News on Friday evening, presents a limited account of the days before the insurrection, and reportshave questioned the completeness of the Pentagon's version of events and the effectiveness of its planning and response. But the memo may well provide a partial roadmap as legislators call for an investigation into how pro-Trump protesters breached the Capitol in a riot that left five people dead, including one Capitol Hill police officer. Three officials who supervise the force have already submitted resignations.

Here's what we know so far, and what we don't.

Nearly A Week Of Preparation

The Pentagon's timeline begins on the last day of 2020, when Washington Mayor Muriel Bowser and another city official delivered a written request for D.C. National Guard support on Wednesday. For weeks, Trump supporters had shared plans on social media for descending on Washington that day to protest the election results as Congress certified the Electoral College votes that sealed President-elect Joe Biden's victory. In the days after, Acting Secretary of Defense Chris Miller met with “select Cabinet Members," the memo says without specifying which, to discuss Defense Department involvement and “potential requirements" for DOD support.

Trump Authorized National Guard Deployment

On Sunday, Jan. 3, Miller and the chairman of the Joint Chiefs of Staff, Gen. Mark Milley, met with Trump. According to the memo, the president “concurs in activation" of the National Guard to “support law enforcement." Miller approved the activation of 340 Guard members the following day.

The details of Trump's conversation with Miller and Milley are not known.

Pentagon Joined Planning Exercise — After Protests Began

Swarms of pro-Trump protesters assembled in Washington on Wednesday morning, starting at the Ellipse to hear Trump speak and heeding his suggestion that they take their complaints to the Capitol, where Congress was meeting in joint session to certify Biden's election. Trump ended his remarks just after 1 p.m.

Around 11:30 that morning, Miller participated in a tabletop planning exercise regarding DOD's “contingency response options," the memo says. While Miller participated in numerous preparatory conversations with local and federal officials in the week leading up to Wednesday, the timeline gives no indication that any formal planning exercises took place before the day of the attack. The Pentagon did not immediately provide an explanation for the eleventh-hour exercise.

Capitol Police Declined Pentagon Support — Twice

Three days before the mob overtook the Capitol, DOD contacted the U.S. Capitol Police to confirm that the force was not requesting backup in advance of the scheduled protests, according to the timeline. The next day, the memo says, USCP officials participated in a phone call with Army Secretary Ryan McCarthy and once again confirmed they did not need the Pentagon's support.

That position only changed at 1:49 on Wednesday afternoon, when USCP Chief Steven Sund called requesting immediate assistance. By then, members of Congress were sheltering in place, with the mob minutes away from breaching the Capitol steps.

It remains unclear what intelligence the Capitol Police, which boasts more than 2,300 employees and a budget of over $400 million, gathered in anticipation of Wednesday's events or why Sund declined to bolster the Capitol's defenses. Sund's resignation was announced on Thursday, and he will leave his position on Jan. 16. Sund and the USCP did not immediately respond to a request for comment.

Mayor Bowser And Pentagon Offer Conflicting Accounts

After Bowser sent her New Year's Eve request for help from the D.C. National Guard, the DOD memo says it approved sending 340 Guard members to support local officials. It further says that on Tuesday, Bowser delivered a letter confirming that Washington officials had all the support they needed.

But a spokesperson for Bowser's office told NBC News that it was McCarthy, not the mayor, who made the key decisions about the National Guard's response, including setting the number of personnel and establishing “that the guard members were not to move East of 9th Street NW," blocks away from the Capitol itself.

Once Mob Entered Capitol, Guard Didn't Show Up For Hours

At 1:26 p.m. Wednesday, with a mob of protesters about to push through police lines, the USCP ordered the Capitol evacuated. Eight minutes later, according to the DOD timeline, Bowser was on the phone with McCarthy requesting an “unspecified number of additional forces." Sund's call to Pentagon officials followed shortly thereafter.

At 3 p.m., more than an hour after the mayor's call, Miller determined that D.C. National Guard forces were needed to reestablish control of the Capitol, and minutes later, he formally approved the full activation of the D.C. National Guard. At 5:02 p.m., 154 guard members left the D.C. Armory to head to the Capitol, where they arrived roughly 40 minutes later.

By 6:14 p.m., law enforcement had successfully established a perimeter around the west side of the Capitol, according to the memo, and at 8 p.m., Capitol Police declared the building secure.