There is no doubt in m,y mind that GCHQ was in fact used by obama to try to circumvent the law, This WILL come out . GCHQ is lying to save its ass. No doubt about it.
I think the info Nunes viewed at the White House will substantiate that.
My theory is that GCHQ was monitoring pro-Brexit Nigel Farage (or the NSA was monitoring him on behalf of the Brits), and Trump’s people were picked up in any correspondence with him.