Trump ignores the problem of white nationalist terrorism because he’s a white supremacist and many members of his base are too. He has encouraged violence and downplayed the threat of terrorists who are inspired by his bigotry. He offered sympathy to New Zealand but didn’t say the word Muslim. Trump’s rhetoric has encouraged anti-Muslim bigotry worldwide.
This is like “very fine people” after Charlottesville. It’s obvious he doesn’t want to deal with the problem and in fact is making it worse. I am much more concerned about white supremacist terrorists than I am about ISIS or immigrants from Mexico and Central America.