The chief of the Capitol Police said he tried 6 times to call reinforcements to deal with pro-Trump rioters but kept getting blocked

• The departing chief of the Capitol Police says he called for backup six times before and during Wednesday's attack at the US Capitol but was kept waiting.
• Chief Steven Sund told The Washington Post he unsuccessfully asked the Senate and House sergeants at arms multiple times for permission to call the National Guard.
• Sund said that he asked the Pentagon for help after the violence started but that Lt. Gen. Walter E. Piatt, the director of the US Army Staff, declined.
• The Guard eventually deployed at 3:10 p.m. and arrived at 5:40 p.m., The Post said, after the violence had mostly ceased.
• Sund told The Post: "If we would have had the National Guard we could have held them at bay longer."

The departing chief of the Capitol Police said he tried six times to summon reinforcements before and during Wednesday's attack by supporters of President Donald Trump but was blocked from doing so by his superiors.

Speaking with The Washington Post on Sunday, Chief Steven Sund said he worried that the protest would turn violent but was unable to get help until the violence was at its peak.

"We knew we would have large crowds, the potential for some violent altercations," he said.

Four civilians and a police officer died as a result of Wednesday's attack, which plunged Washington into chaos and prompted calls for President Donald Trump to be impeached for his role inciting the violence.

Read more: Secret Service experts are speculating in group chats about how Trump might be hauled out of the White House if he won't budge on Inauguration Day

From 1 p.m. ET on Wednesday, as Trump supporters gathered at the perimeter of the Capitol, Sund made a string of requests for backup, he told The Post.

Here are some of the calls he described. Only the first brought immediate help:

• At about 1 p.m. Sund called Robert J. Contee, the chief of police for Washington, DC, and 100 officers were deployed.
• At 1:09 p.m. Sund called House Sergeant at Arms Paul Irving and Senate Sergeant at Arms Michael Stenger to get permission to deploy the National Guard. He said that the pair told him they would "run it up the chain" but that he didn't hear back.
• After that Sund called Irving twice more for a follow-up.
• After that Sund called Stenger once more for a follow-up.
• At 2:10 p.m. Sund got approval from Irving to call the Guard - but was blocked again at the next step.
• At 2:26 p.m. Sund joined a call with Pentagon officials and asked them to deploy the National Guard. He was told no by Lt. Gen. Walter E. Piatt, the director of the Army Staff.

Sund recalled telling Piatt: "I am making an urgent, urgent immediate request for National Guard assistance. I have got to get boots on the ground."

Sund said Piatt responded: "I don't like the visual of the National Guard standing a police line with the Capitol in the background."

The US Army did not immediately respond to a request for comment from Insider.

During the call, Sund repeated several times that the situation was "dire," John Falcicchio, the chief of staff to Mayor Muriel Bowser of Washington, told The Post.

Jonathan Hoffman, a Pentagon spokesman, said the Capitol Police did not request help until after the pro-Trump protest had turned violent.

"We rely on Capitol Police and federal law enforcement to provide an assessment of the situation, and based on that assessment that they had, they believed they had sufficient personnel and did not make a request," he said last week, per The Post.

The National Guard was eventually deployed by Christopher C. Miller, the acting defense secretary, at 3:10 p.m., according to a Department of Defense timeline, The Post reported.

Those troops arrived didn't arrive at the Capitol until 5:40 p.m., however, long after most of the violence had ceased, The Post said.

The Post said Sund described warning of the threat of violence days before.

According to The Post, Sund said he asked House and Senate security officials two days before the attack whether he could request that the National Guard be placed on standby. He was denied.

Irving, the House sergeant at arms, told Sund he didn't like the "optics" of essentially broadcasting that authorities were expecting an emergency, Sund said.

"If we would have had the National Guard, we could have held them at bay longer, until more officers from our partner agencies could arrive," he told The Post.

Sund announced his resignation on Thursday after widespread criticism of the official response to the attack. His last day is set to be Saturday.