Its obvious what happened on Jan. 6: Supporters of outgoing President Donald Trump attacked the Capitol because he told them the 2020 election had been stolen from him.

But there are some questions that could use authoritative answers. What did the president do before and during the Capitol attack? Why didnt the National Guard show up until several hours after the riot started? And what needs to be done to prevent another insurrection?

Senate Republicans blocked an attempt to find answers, filibustering debate on a bill to create a bipartisan commission that would dig into the Jan. 6 attack. The commission, approved by House Democrats and 35 Republicans last week, was to be modeled after one that investigated 9/11 and made several recommendations, including the creation of a new director of national intelligence post to oversee federal intelligence agencies.

Forming commissions isnt unusual for Congress lawmakers have created more than 150 commissions since 1989, according to the Congressional Research Service . Theyre usually staffed by well-known policy experts rather than lawmakers themselves.

In addition to recommendations, commissions can provide authoritative accounts of major events in a way that lawmakers themselves cant, both because most people dont like Congress and also because lawmakers may have shortsighted political goals that make the truth inconvenient.

The deeper value to society is going to transcend whatever partisan values might seem important in the moment, said Scott Knowles , a historian of disasters and their aftermaths.

Even though this particular commission is meant to investigate an attack on members themselves, in their own place of work, most Republicans oppose it. They insist its partisan and meant to hurt Trump, who is still a major influence on the party despite his scandal-plagued, single-term presidency.

Plus, they argue, who needs it? The Capitol attack is already under investigation by law enforcement, which is prosecuting people who breached the building, and Congress has held hearings on it. The same was true of past commissions, however. The 9/11 terrorist attacks were under investigation from law enforcement and congressional committees; that didnt stop Congress from creating its commission, which uncovered material that committees missed.

Its impossible to know for sure what a commission could learn, as Knowles noted. You cant always predict what theyre going to find, like any kind of investigation, he said.

But there are major unanswered questions about the attack that deserve a closer look.

What did, or didnt, Trump do to stop the riot?

Trump told House Republican Leader Kevin McCarthy (Calif.) during a phone call that the rioters were left-wing agitators, and when McCarthy pointed out that they were Trump supporters, the president reportedly said, Well, Kevin, I guess these people are more upset about the election than you are.

Thats according to Rep. Jaime Herrera Beutler (R-Wash.), who spoke with McCarthy shortly after Trump did.

To the patriots who were standing next to the former president as these conversations were happening, or even to the former vice president: if you have something to add here, now would be the time, Herrera Beutler said in a February statement . (She voted in favor of forming the commission last week.)

McCarthy hasnt spoken in detail about the conversation, but he said Thursday he would testify about it if a commission asked him.