Oh, I don't think the kompromat angle per se could hold up. It's one thing for the intel community to get the nod from sources they trust (and pay) in the Kremlin -- "yes, it exists, it depicts this and that." It's another thing entirely for them to get their hands on it. I imagine the bodies/arrests accumulating around the Steele memo are serving as a fairly strong deterrent of future disloyalty within the Russian security services.
But if there was contact, on this or any other illicit topic, between Trump and FSB/GRU/etc., that's what would get him. For example, if the recording delivered to Brennan really did capture agents of the Russian government discussing financial aid for Trump or his campaign, or collusion with the Trump campaign re: the hacks, then that should be enough.
As an aside, I do believe the kompromat story. In fact I believe it's becoming difficult to seriously doubt it in good faith. Take what we know about Trump: he is pussy-grabbing silver-spoon nihilist undeterred by something like the marital status of his target (to say nothing of her consent). A NYDN columnist said in 2001 that he brags about "banging" girls who "have no morals" in Russia specifically. So: has Donald Trump done repulsive sexual shit in luxury Russian hotel rooms? Yeah, undoubtedly.
Now take what we know about the FSB: they record what goes on in hotel rooms, particularly expensive high-status penthouses & suites where celeb clowns might expose themselves in all kinds of useful ways. The KGB used to actually run the Soviet state travel agency specifically so that they could collect kompromat. So: did the FSB record whatever Trump was up to? Yeah, undoubtedly.
Does this square with the related evidence, like Trump's behavior during the Superbowl interview? Yes: almost too perfectly.
Edit: factor in what the CIA told Paul Wood & what the arrests/murders suggest re: Steele's sources and there you have it.