Hope not. Possible, though.

100% of every possibility regarding NSA surveillance has gone from "That's possible, but surely they wouldn't" to "Wow, they did, and did it bigger than anyone imagined."

Why wouldn't that include suppression of political initiatives that could interfere with the NSA's mission?

It's conceivable, but it would be a considerable step-up from what has been leaked so far.

I am more willing to accept the possibility if it's shown to be true that they've been conducting surveillance on US politicians and officials. Not that spying on foreign politicians is good or moral, but the reasons are different at least.

Why would you consider it "a considerable step up?"

We already know that surveillance in the US is pervasive. And that includes politicians, judges, and everyone else in government.

It's just a small step to using that information for safeguarding NSA's mission.

Well, you're suggesting they are actively engaging in blackmail and political manipulation to retain their position. Even if they do have the information to blackmail in many cases, it does not mean they actually are.

Perhaps I'm just naive, but I like to think at their core they're not so immoral as to degrade themselves to that sort of behavior.

Just as I am certain they do not think of anything we are certain that they do a crime, neither would they think of using available information to influence political support a crime, either.