[michaelt]

  how is that going to protect the US? [...] perpetrators
  will not transport any digital devices with incriminating
  data.

Options include:

1. Bad guys with imperfect opsec (I see in your unallocated space there's a deleted TAILS ISO... onto a watchlist with you!)

2. Friends and relatives of bad guys (I see your nephew e-mailed you holiday photos from cybercafes near two different suspected terrorist training camps... onto a watchlist with him!) a bit like social media companies' 'shadow profiles'

3. Non-terrorist targets, like good old corporate espionage and political blackmail (Oh, you're a journalist/oil industry exec/prostitute? Let me just take a copy of your contacts, records and reports)

[sneak]

Pretty sure from leaked XKEYSCORE rulesets, anyone who downloaded or googled "tails" is already on that list.