Clapper lies. But you can totally believe him when he says...
By every account from former employees--and a few current employees who have secretly leaked information--the NSA monitors all phone calls in the U.S., looking for "trigger words" ("attack", "chemical weapons" etc).
So...director Clapper testified to congress a few years ago. He was asked if the NSA did anything remotely *like* that.
He denied that the agency did anything like that.
So...if he'll lie to congress (which he did), how can you believe him when he a) claims the Russians interfered with the 2016 election; or b) claims the Obama administration didn't order wiretaps on Trump's phones?