DC police have 3,800 officers [2] which is quite a few considering Washington DC has a population of 705,000 [3] (the national average is 470 people per officer, while DC has just 185 people per officer) and of course only so many of them can be on shift at a time.

A large protest can have 100,000-500,000 protesters [1]

So even if 95% of protesters are peaceful, a mere 5% inclined towards disorder can easily outnumber the local police. So it's not so crazy they'd need to call backup from somewhere. Why it's so common to deploy the national guard rather than cops from other nearby jurisdictions I don't know.

[1] https://en.wikipedia.org/wiki/List_of_protests_in_the_United... [2] https://en.wikipedia.org/wiki/Metropolitan_Police_Department... [3] https://en.wikipedia.org/wiki/Washington,_D.C.

Washington, D.C. is very much a commuter and tourist town. Its population might be 705k, but the average number of people in the city on a given day is much higher. Tons of people who work in D.C. live in Virginia and Maryland and commute. I don't think I need to really get into why its kind of a major tourist destination. It does not surprise me they have a much higher people per officer than the average town.

True - what I'm trying to say is: Although DC cops can easily be outnumbered by protesters, in pure numbers DC isn't under-staffed by national standards.

Even the most self-sufficient of cities would find their cops outnumbered in such a situation.

It's not that they couldn't secure the capitol, it's because they didn't want to and are sympathetic to the rioters. The same way us devs look at requirements we know how to do but don't want to and instead say:

"Nope, can't do that, not enough timeslices on mutex semaphore of a monadic type for me to transpile that functionality of changing the color of the background"