https://www.politico.com/news/2021/12/06/jan-6-generals-lied-ex-dc-guard-official-523777
So here's the head of the DC national guard saying that they were purposely delayed in their response and that the people from the army who testified in front of the jan 6 committee were, his words, "absolute and unmitigated liars".
Here are jan 6 rally organizers saying they knew before it happened that the rally was going to involve an unpermitted match in the Capitol. They say they called white house chief of staff Mark meadows about it and were ignored. The person who claimed to have made the call now says they didn't and the white house was unaware of the plans to march on the capitol. Given the number of rioters who showed up in bespoke tshirts that said "storm the capitol" it's fair to say that if the white house didn't see this coming they were the only ones who didn't. The article also establishes that Enrique tarrio, Alex Jones and Nick Fuentes were there and that organizers put up with their openly abhorrent beliefs because they can "push bodies where we point". This is relevant because it means that people we've proven were in contact with the white house before 01/06 were there to cause a riot and knew it.
The above link also shows that capitol police knew what was coming. The released a memo on Jan 3 saying “Stop the Steal’s propensity to attract white supremacists, militia members, and others who actively promote violence, may lead to a significantly dangerous situation for law enforcement and the general public alike." An internal email from 12/31 said that rally permit requests were “being used as proxies for Stop the Steal” and that those requesting permits “may also be involved with organizations that may be planning trouble” on Jan. 6.
Another thing of note from that source is that no march on the capitol was permitted, but plans among organizers including those known to have been in direct contact with the white house publicly talked about the rally ending in a march on the capitol. It wasn't until after those plans were published that Trump tweeted that he would personally attend the rally.
It's also important to know that the DC national guard is unique in that it's deployment is managed by the white house directly, rather than by state governors as other national guard groups are. The above source says that capitol police requested national guard support 6 times, including after violence erupted, and were denied all 6 times. Muriel Bowser, mayor of DC at the time, had also requested NG support ahead of the rally and had been denied.
So the white house was aware in advance of the rally, including that it would involve an unpermitted march on the capitol. Some organizers were so concerned that violence would erupt that they reached out to white house chief of staff mark meadows about it. They knew violence was coming. After the more openly violent elements announced that they would illegally march on the capitol, Trump tweeted that people should attend the rally and that he would be there personally. They took steps to amplify the violence. Trump also had the power to deploy the DC national guard. The guard was requested both before the rally by the mayor of DC and during the violence 6 times by capitol police. These requests could have been granted by Trump, but were instead denied. The trump white house took steps to hamper the response to the violence.
What else would you need in order to believe that this was a planned assault on democracy, coordinated directly with the white house and designed to take advantage of a legitimate peaceful protest?