For years the anti-gun people talked about terrible it was that people could buy guns even if they were on the terrorism watch list:

• Just what I would expect (2007)
• Where’s the due process? (2007)
• Due process? Who needs it? (2009)
• Gun cartoon of the day (2010)
• People On Terrorism Watch List Not Blocked From Buying Guns (2013)

The Brady Campaign even coined the phrase “terror gap”. Their web page (http://www.bradycampaign.org/legislation/backgroundchecks/terrorgap) has since been taken down and the phrase cannot be found on their website (but you can find it on bradynetwork.org) but it was an issue they tried to get traction on (see also this search result).

And during that entire time we tried to tell them such action by the government would violate due process protections. They ignored us.

We were right. Again. And it is not just on the constitutionality of using such a list to deny someone their specific enumerated right to keep and bear arms. The present implementation of the “no fly list” itself is a violation of due process:

A federal judge on Tuesday found unconstitutional the methods by which the federal government places U.S. citizens and legal permanent residents on a “no fly” list without letting them see the evidence against them, or letting them contest it.

…

“Accordingly, on this record the court concludes the absence of any meaningful procedures to afford plaintiffs the opportunity to contest their placement on the No-Fly List violates plaintiffs’ rights to procedural due process.”

The right to travel isn’t clearly spelled out like the right to keep and bear arms. A judge could (and may still) find a weasel worded way of saying you don’t have to be to able travel by commercial airplane as long as there exist private airplanes you can hire. Hence due process protections for the right to keep and bear arms should be even greater than for the right to travel.

This also has implications for mental health restrictions on the right to keep and bear arms which is something the anti-gun people are trying to implement.