If you have the goods on Trump, why leave FISA out of the loop? The court was formed back in the 80's or 70's for the purposes of warranting searches involving foreign governments. In fact, that would be the first thing to do, if some form of espionage is suspected between Trump and the Russians.
No matter how you slice it, it doesn't come out well for democrats and Trump haters.
If DOJ was turned down by FISA for lack of evidence---well, there goes your conspiracy theory.
If FISA issued the warrant, then Trump WAS tapped. Which raises the question of their findings. If they have something, why are they sitting on it?
My guess is they have nothing to show or they would have let it out in October.