Earlier quoted context omitted.
Can you explain how this is consistent with his political alignment? Because Bernie Sanders (regardless of how you feel about him) has voted consistently against increasing the surveillance state. Hence why his vote wouldn't have mattered, because it would've been a NAY vote and NAY votes don't have any affirmative power.
The vote is on a plan to REQUIRE a warrant. If he'd voted, he would have voted YEA , to pass this bill requiring a warrant, because he does not want to increase the surveillance state (on that we agree!) It's "yea" for requiring warrants, and "nay" for warrantless surveillance (which is somehow the law of the land now? When did I miss this??)
I suspect Bernie's abstention is because he thinks reauthorization is equally unacceptable with or without the condition.
Procedurally, he could vote yes on the amendment and still vote on the bill, and there's an argument that not doing so is making the perfect the enemy of the good (or at least the barely decent the enemy of the mildly less oppressive of two oppressive options), but it's kind of hard for me to get mad at Sanders for not collaborating in putting lipstick on this particular totalitarian pig of law. One can maybe rationalize the USA Patriot Act in the context of it's time, it's much harder to rationalize the USA Freedom Act’s deliberate after-the-fact authorization of much of the illegal blanket surveillance that went beyond what the original Patriot Act authorized, and it's far harder to rationalize the current reauthorization of the combination, with or without minor tweaks.