How will he equivocate though if he didn't equivocate in his memos (as they are going to be subpoenaed)?
I doubt very much that his memo is explicitly damning for two reasons.
1. What we've had reported as hearsay about the memo wasn't particularly damning. It certainly didn't sound like a direct order to halt the investigation into Flynn, and Comey obviously didn't take it that way, because he didn't halt the investigation into Flynn.
2. If Comey thought Trump was obstructing justice, he had a duty to report it, and he didn't do that. Now he could say that Trump's message was sufficiently vague that he thought Trump could have been obstructing justice but wasn't sure, and so he didn't report it for that reason, but such an explanation leaves Trump plenty of wiggle room.
There's no doubt that we are all speculating and we'll have to wait and see what Comey says.
I have two additional thoughts on the matter, which are:
Between Trump's potentially criminal conversation with Comey in the affair with Flynn and Bill Clinton's potentially criminal conversation with Loretta Lynch related to the investigation into his wife, there's a disturbing disregard for , at a bare minimum, the appearance of propriety. Even if neither did anything wrong, it looks so bad that erodes public trust. And public trust in our political institutions is something our political elites seem to take for granted, but once it is gone it is very hard to rebuild.
If Comey testifies and takes down Trump, he will have destroyed the political prospects of the Democratic nominee and the Republican nominee. J. Edgar Hoover served under five (four?) presidents, none of whom trusted him but none f whom dared to cross him. I don't think that kind of power should necessarily rest with an unelected official, who cannot be fired by an elected official without massive political fallout. Both Dem and Republican voters have called for Comey's head, yet firing him may have been a bridge too far. Whatever Trump's fate, he may well deserve it, but we shouldn't overlook how poorly Comey has behaved in using these well archived memos as political payback.