A nationalist is not the same thing as a patriot, but a lot of politicians try to spin it as if they are, and if that's what he meant, fine. He could have gotten away with "nationalists are Americans."
But white nationalist, specifically? No. This is universally understood to deserve people who think that whites are superior to all others and deserve more from society, and all others deserve less and should be dominated by whites. This is the Aryan Brotherhood, the American Nazi Party, and the Klan. Anyone who backs them is a piece of shit of the highest order, and should be an enemy to all Americans, full stop.
In all likelihood, I think he meant to say "white people, who are American nationalists," and he just got ahead of himself in the moment. CNN apparently did report that he later clarified with a four-word "White nationalists are racists" nullifier later that day, and other Republicans did give him a rack of shit for it, which politicians don't always do to their own party. Still, though, that's either a massive gaffe or a super-damning Freudian slip that should have sent him running to the nearest mic to clarify, over and over again, that he did not mean to just say "Klansmen are welcome."
The worst part about this is that a lot of people just don't care that a sitting US Senator appeared to accept white nationalism, even if they did see the super-short "I didn't mean it" walkback. That tells me that a lot of people are either distracted, dumb, or sleepy enough to let white supremacy gain a foothold in the highest levels of our country, or they are white supremacists themselves.
