If he knew / suspected she was a spy, yes, absolutely. If she was given access to confidential information, yes, absolutely.
If he thought it was a romantic relationship, fine, that doesn't affect me / NVDA / America.
Obviously he should stop now that he knows! But if he didn't at the time, you know, I think I can still trust him to make computer chips.
"Bad judgement" is a tool used in political rhetoric used to blame someone when there's nothing of any substance to blame them for.
However, all of this changes if it turns out that he gave his lover's company any kind of preferential treatment or that she was involved in China related lobbying.
This is what the investigation will focus on in my opinion. If they find anything at all then he will have to resign.