How many American citizens are on the terrorist watch list?

• Are any on the list in error? 
• What if 90% are foreign? They can't buy guns here under current laws, right? 
• How do you deprive a citizen of a constitutional right without a trial? 
• Do they go to jail or just lose their 2nd amendment rights? 
• Are we safer if they use a grenade or bomb? 
• Are there other rights we can lose for being on other lists--like being members of a church, for instance, and therefore can't exercise our religious rights? 
• Or rights to assemble? 
• Were Tashfeen Malik and Syed Rizwan Farook (San Bernadino) on a terrorist watch list?  
• Was Omar Mateen on a terrorist watch list?
•  How does a terrorist watch list work if we're afraid of Muslims or being called Islamophobic?

Farook was a U.S. citizen; Malik a permanent resident; Mateen was U.S. born. Mateen had apparently been a trouble maker since elementary school, but was able to get security clearance to work for a Homeland Security contractor and his status as a Muslim protected him from co-workers complaints.