https://www.justice.gov/usao-ma/pr/mit-professor-arrested-an...
https://www.justice.gov/opa/pr/us-navy-officer-his-wife-and-...
https://www.justice.gov/opa/pr/former-cia-case-officer-charg...
https://www.scmp.com/news/china/diplomacy/article/3104566/ch...
https://www.washingtonpost.com/national-security/us-citizen-...
Edit: Not to mention the internment of Japanese Americans during WWII.
I had a Lance Corporal who worked for me who's father was a member of the Aryan Brotherhood. He had to get a waiver for his security clearance because he had a direct connection to a known criminal and racist organization. "Do you, or any of your family, have connections to the CCP?" should probably be a question added to the next version of the SF86 ( https://en.wikipedia.org/wiki/Standard_Form_86 ), and should trigger additional scrutiny. I'm not sure what is measures are in place now but they are clearly insufficient.
Edit: also, is there any evidence that banning people of a certain birth place is actually effective? We already do background checks, and if those don’t screen out the risks, why would an additional blanket ban help?