CBRN (chemical, biological, radiological, and/or nuclear) attacks have been used by both state and non-state agents in warfare and insurgent activity. For example, ISIS, the United States, and the Syrian state have all been known to use chemical weapon attacks. The United States is particularly known for its use of white phosphorus in Iraq, which has led to absolutely devastating consequences for the Iraqi people. In relation to the use of a CBRN attack within US soil, the chance of a non-state agent using this means of attack does not seem particularly high given the historical precedent and current reality of states being far more likely to use CBRN attacks against opposing forces and/or civilians (such as the actions of the United States in the nuclear bombing of Japan, or the use of chemical weapons in Vietnam or Iraq).
In the United States, attacks by non-state actors tend to come in the form of firearms and simple explosive devices. There has absolutely been a rise in the rate of white supremacist mass shootings and attacks in the United States, particularly since the deadly Unite the Right white supremacist rally of 2017 in Charlottesville, Virginia, left one woman murdered by a Neo-Nazi, with many more severely injured. Since then, white supremacists have been responsible for mass shootings attacks such as the deadly El Paso, Texas, shooting, the Gilroy, California, food festival shooting, the Pittsburg, Pennsylvania, synagogue shooting, and the fire-bombing of the Highlander Center near Knoxville, Tennessee. These are just a handful of examples of recent attacks by white supremacists.
However, so far, none of these attacks have been CBRN attacks. It appears unlikely that these attacks will decline anytime soon, with ever-rising white supremacist ideology and state-based oppression of people of color, such as the horrifying use of concentration camps on the US border against migrants. If a CBRN attack does originate from within US soil, it would be unsurprising if this attack originated from a white supremacist individual or organization, given the prevalence of mass shootings being attributed to people with this ideology.