But national security is. All they would need is a flimsy justification that the person was stealing state secrets (like Trump) or organizing a terrorist attack, which could include any contact with an armed or paramilitary group that’s planning a protest. They could use state influence to coerce that group to take action, and the records of that planning process would be inadmissible per this ruling. It’s not hard to come up with superficial reasons that do align with Constitutional obligations.
Edit to add: Hell, just look at the McCarthy era, or the Iraq war. It’s not hard at all for a sufficiently shameless group of politicians to gin up a moral panic about national security. They don’t even need evidence, they just need motive. We’re real fucking close to the government being able to legally assassinate purported communists for subversion.