That’s only partially accurate. Trump’s belief that government lists can take away your 2nd amendment right is not new.
“If somebody is on a watch list and an enemy of state and we know it’s an enemy of state, I would keep them away, absolutely.”
http://www.cnn.com/2015/11/22/politics/donald-trump-ben-carson-guns-terror-watch-list/
He’s held this position for months or longer.
I think what you are missing here as far as the argument goes is what is the process for putting people on the terror watch list? Its a secret and we all need to know the criteria. Otherwise the govt could put every combat vet and every tea partier who ever made a cryptic comment on social media on the terror watch list and voila’ you have millions denied their rights under the second amendment.