Under questioning by Alexandria Ocasio-Cortez, Acting Defense Sec Miller revealed that there was a three-hour delay between when the Capitol Riot started to when the National Guard were finally being deployed.
Requests for the National Guard had come from the Mayor of DC, the local National Guard commander, from the Sargent at Arms for the Capitol and from Nancy Pelosi and Chuck Schumer’s office but it wasn't until Miller had a conversation with Mike Pence at 4:08 pm that the Guard was finally authorized at 4:32 pm.
Miller’s exact reason for this delay was rather vague and nebulous but we do know who didn't give him a call. He didn't get a call to release the Guard from Donald Trump. After rules established following the deployment of the Guard against Black Lives Matter in DC during the summer, the authorization had been kicked up the chain of command to the White House. If Trump (or Pence) didn't make the call, the Guard wasn't coming.
Trump was watching the Insurrection unfold on live TV. He had a conversation with Kevin McCarthy where after first claiming the attackers were “from Antifa” he told him “I guess these people are more upset about the election than you are.” He didn't release his weak statement to "go home, we love you” until nearly 4pm. Twitter locked his account for his encouragement of the riot at 4:02 pm.
Trump sat on his hands this entire time. It was because Pence finally stepped in that the Guard were deployed at all. Frankly, if Trump had called for the Guard, it probably would have been to have them help the protestors, not the police. Based on the discussion that Miller had with Trump on Jan 3rd, very likely those were the "optics" that Miller was concerned with.