Testifying on Tuesday in the first congressional hearing on the US Capitol attack, the chief of Capitol police who resigned over the riot said the pro-Trump mob which stormed the building “came prepared for war”. Merrick Garland would seem to agree. In a confirmation hearing on Monday which set the scene for Tuesday’s session before the Senate homeland security and rules committees, Joe Biden’s nominee for attorney general said he would expand the criminal investigation into the 6 January assault, telling Congress domestic terrorism is a greater threat to American democracy than it has been for decades. Before the Senate judiciary committee, Garland described the insurrection of Trump supporters and white supremacists as “a heinous act that sought to disrupt a cornerstone of our democracy”. He said his first act if confirmed would be to focus on domestic terror. Describing the events of 6 January as “not necessarily a one-off”, Garland, currently a federal judge, pledged to use the full powers of the justice department to prevent a repeat attack. “I intend to look more broadly at where this is coming from, what other groups there might be that could raise the same problem in the future,” he said. On Tuesday, the two top officials in charge of securing the Capitol the day of the deadly assault were called to give evidence to Congress. Paul Irving, the former sergeant-at-arms for the House, and Michael Stenger, his equivalent for the Senate, both resigned after the breach. Their testimony marked the start of a congressional investigation into security lapses behind the insurrection. Stenger said: “This was a violent, coordinated attack where the loss of life could have been much worse.” Irving said: “Based on the intelligence, we all believed that the plan met the threat, and we were prepared. We now know we had the wrong plan.” Two other officials, former Capitol police chief Steven Sund and the acting chief of police for Washington’s Metropolitan police, Robert Contee, also offered testimony. Sund also resigned in the wake of the catastrophe. “These criminals came prepared for war,” Sund told senators. Sund and Contee both expressed astonishment at delays at the Pentagon after the appeal went out for reinforcements at the Capitol and the deployment of the national guard. Sund said: “I was certainly surprised at the delays that I was hearing and seeing.” Contee recalled a phone call between Sund and Pentagon officials in which Sund could be heard “literally pleading” for backup. When no immediate affirmation was forthcoming, Contee said, “I was just stunned. I have officers who are out there literally fighting for their lives.” A captain in the Capitol police, Carneysha Mendoza, described 6 January as “by far the worst of the worst” of all the days she has worked. “We could have had 10 times the amount of people working with us, and I still believe the battle would have been just as devastating,” Mendoza said. The riot arose from a gathering to “save America” and “stop the steal”, inspired by Donald Trump’s lie that the 2020 presidential election was rigged and widely advertised on social media. Trump headlined the rally, delivering an incendiary speech which he had billed weeks earlier with a tweet saying: “Big protest in DC on 6 January. Be there, will be wild!” The riot that ensued left five dead. A woman trying to break into the House was shot dead by police. A Capitol officer, Brian Sicknick, died after being struck with a fire extinguisher. In the Senate on Tuesday, Rob Portman of Ohio, the top Republican on the homeland security committee, noted that two officers have killed themselves since. “We will never forget the service and sacrifice” of those officers, Portman said. He was one of 43 Republican senators to vote to acquit Trump in his impeachment trial on a charge of inciting the insurrection. The aggressive approach to investigating the 6 January riot, coupled with Garland’s testimony, signals a sharp change of tack under Democratic leadership in Washington. Garland’s emphasis on white supremacy, and his clear labelling of it as domestic terrorism, marks a departure from the leadership of Trump and Mitch McConnell, the Senate Republican leader, who tended to minimize the danger or, in the case of the former president, actively refuse to condemn far-right and racist groups. Garland’s hearing saw him quizzed on his definition of domestic terror by one of the Republican senators accused of egging the seditionists on. Joshua Hawley of Missouri was photographed with a clenched fist in a display of solidarity with the “stop the steal” crowd outside the Capitol, shortly before violence erupted. Hawley asked Garland if he thought violence against federal property during racial-justice protests was a form of domestic terrorism. Without mentioning Hawley’s actions on 6 January, Garland replied that to disrupt democratic processes, as in the Capitol insurrection, did fit the definition. “Attacking a courthouse at night” did not. Garland is a credible voice on domestic terror. He was lead prosecutor of the Oklahoma City bombers in 1995. In his testimony he drew a line from the Capitol insurrection back to Oklahoma City, where 168 people were killed, and on to the “battles of the original justice department against the Ku Klux Klan”. Tuesday’s testimony by the former Capitol security chiefs was arranged by Democrats Amy Klobuchar of Minnesota and Gary Peters of Michigan. The senators questioned their witnesses about why they seemed caught off guard. The joint hearing was just the beginning of an anticipated welter of investigations. Though Trump was acquitted by the Senate, Democrats remain determined to review the actions and mistakes that led to the assault. A bipartisan independent commission may also be convened. “This is certainly not the last hearing we will have on this attack,” Klobuchar said on Tuesday.