The rioters had begun vandalizing, looting, breaking in and setting fire to buildings directly adjacent to the federal courthouse before federal agents arrived to protect the courthouse. Active defense of the courthouse seems justified, and more than that, it is legal.

May 31st: Looting and fire at Justice Center, adjacent to federal courthouse: https://www.portlandoregon.gov/police/news/read.cfm?id=25081...

June 27th: Some feds arrive in response: https://www.oregonlive.com/news/2020/07/evidence-shows-portl...