Republicans in the U.S. Senate are a threat to our democracy.

Here’s the latest proof: Republicans are using the Senate’s filibuster rules to stop Congress from creating a commission to investigate the deadly Jan. 6 attack on the U.S. Capitol.

The filibuster has a long and dishonorable history. It was used over and over to block passage of civil rights laws. Now it is being used to undermine democracy in another way.

On one level, we all know what happened on Jan. 6. A violent mob of Trump supporters tried to stop Congress from affirming the victory of President Joe Biden and Vice President Kamala Harris. They wanted to overturn the results of the election and keep former President Trump in power.

That mob had blood on their minds. And they ended up with blood on their hands. Fortunately, they didn’t get a chance to hang then-Vice President Mike Pence or to kill House Speaker Nancy Pelosi or other members of Congress they were targeting. But five people died that day. And more than 100 Capitol Police officers were wounded. One lost an eye, one lost fingers, some suffered brain injuries.

Many are traumatized by a battle they didn’t expect they would have to fight.

We also know what fueled the rage of that mob: Mr. Trump’s big lie — the lie that Mr. Trump won the 2020 presidential election and had it stolen from him and his supporters by Black voters and corrupt election officials. Everyone who spread that lie helped to light the fuse and fan the flames that exploded on Jan. 6.

Those who committed violence must be charged, tried, convicted and sent to prison. And the whole enterprise — those who incited violence and those who planned it — must be thoroughly investigated. People must be held accountable. The best way to do that is with a bipartisan panel committed to finding the truth.

Thanks to online activists and journalists, we are learning more about what happened that day. Regular people are helping identify those who committed violence and the U.S. Justice Department is bringing criminal charges against them. Rep. Jamie Raskin, a Democrat from Maryland, and his colleagues have been holding hearings about the threat of violent white supremacy and the involvement of extremist militias on Jan. 6. But there is much we don’t know.

U.S. Sen. Mitch McConnell, the leader of the Senate Republicans, is trying to protect Republicans running for election in 2022 from having to confront the truth. And while wounded police officers and family members of an officer who died that day went from office to office asking Republican senators to support a commission, Sen. McConnell was calling in favors to stop it from happening.

Some other congressional Republicans have been spitting in the faces of those officers and family members by downplaying what happened that day. One even said the rioters were just visiting the Capitol like tourists.

How many tourists bring a gallows and lynching noose with them? How many smash down doors and windows in their attempt to get their hands on members of Congress?

We cannot let this happen again. History tells us that the best predictor of an eventual successful coup is a recently failed one. Militia groups and other extremists are out there planning more violence, fantasizing about starting a new civil war. If we’re going to stop them, we must learn the whole truth about Jan. 6. We must hold people accountable.

The writer, a former president and CEO of the national NAACP, serves as president of People for the American Way and the People for the American Way Foundation.