Acts of domestic terrorism by white supremacists/nationalists has been public knowledge here for a while. I've posted several articles myself since 9/11 those have groups have posed the greatest threat.
Have you noticed these white supremacists have committed murders in Charlestown, Charlottesville, Pittsburgh, Kenosha, there are others. I'm doing this from memory. Not criticizing but if you are unaware of these you should should be aware. I would say that to anyone.
Not you included but a lot of people who don't know/remember this is because they are living a right wing media bubble. Listening and believing Fox News and Trump begets ignorance.
The Columbine shooters had originally intended it to be a bombing and wanted to outdo the Oklahoma City bombing, which was itself in response to Waco (and Ruby Ridge, another major milestone for White Supremacist leaning right wing gun nut dumbasses). While the Columbine shooters didn't seem to exactly be white supremacists (one of them even wrote about how he felt that racists should be killed in very sadistic manner), there were several Nazi links (I think some early talk was that it might be related to Hitler who killed himself on 4/20, but they'd intended it to be on 4/19 but couldn't get the ammo in time for the 19th; however I think both of them owned some Nazi memorabilia and discussed some adulation for Hitler), and they were planning it to be on the anniversary of the two aforementioned events, which are basically Easter for American White Supremacists, so it certainly was inspiration for it.
White supremacist violence has been a major issue in the US for literally centuries and it regularly bubbles up into intense terrorist acts.
America has a Nazi past that needs to be addressed - I've pointed it out several times on here, but the Nazis got many of their most heinous ideas from America (propaganda techniques, eugenics, concentration camps, even the gas chambers). Hell, even after America demonized the Nazi (and Japanese) medical torture, it perpetrated its own and many people aren't even aware of it having happened. Granted, America's white supremacist problem existed before the Nazis and fed it, it is baffling to me how few people even know the simple links between the Nazis and America, or that America did basically all the horrible shit we view the Nazis so poorly for.