No need to imagine, it literally happened this election cycle: http://www.cnn.com/2017/09/18/politics/paul-manafort-governm...

Whether the renewal to continue spying into early 2017 was (figuratively) warranted is debatable, but with the official reasoning largely classified, the public may never know.

Manafort had been under investigation since 2014. The Trump campaign hired him while he was being surveilled. That could happen from a plain old court issuing a surveillance subpoena. I think FISA should always require court approval. No blanket approvals like were going through phone companies. But court approval on an individual basis is how we've always done legal investigations.

The problem is that people don't want to give up power while they have it, even if it means their opponent gets it next, and even if there's no next-next because your opponent uses it to ensure you never take power again.

There's now substantial evidence that this is exactly what happened with the Obama administration and Trump's campaign. The former used an unverified dossier as an excuse to begin surveillance via FISA. So this isn't even a theoretical issue.

Before anyone grabs a pitchfork, focus on the issue at hand and not the current politics. Doesn't matter who's in the White House - friend or foe, would you want them to have this power?

Citation please, as far as I know there is zero evidence that this happened.

But for the bigger issue, yes it is a thing that needs to be controlled.

Concrete proof has not emerged. Right now it's at the "numerous senior sources say..." level of reporting. The full answer is now known by Congresspeople but it's classified [0]. We'll see if it gets leaked. It's not proven but I certainly wouldn't say zero evidence; reports at this "truth level" happen all the time, and are widely circulated and trusted.

Circumstantially, I think strong evidence that this happened is the Trump team's behavior after he was briefed by the NSA director, Admiral Rogers. The day after their confidential meeting, all relevant activities were immediately moved out of Trump Tower.

Anyway, this is off-topic and is a testy topic as it is so I apologize for the tangent. On topic I agree it shouldn't be possible for anyone to do this, no matter their politics.

[0] http://www.washingtonexaminer.com/byron-york-yes-congress-ha...

The second sentence in the linked article is this: "The Foreign Intelligence Surveillance Court issued the warrant, the official said, after investigators determined that Mr. Page was no longer part of the Trump campaign, which began distancing itself from him in early August."