That transcript from the Washington Post of McCarthy and Ryan is eye-opening. But here's the thing - I think McCarthy's defence that he was just joking will fly. (I actually think he was joking, albeit the sort of awkward, half-terrified joke you tell about something that deep down you suspect is true and that suspicion is scaring the shit out of you - Freud would have a field-day!)
I think it's a good thing to remember what's actually required. A simple majority is enough to bring impeachment proceedings, but a 2/3 majority in Senate is required for them to go through. What is out there at the moment is a massive pile of circumstantial evidence. It stinks to high heaven. It would convince Democrats in Senate "on the balance of probabilities", but it wouldn't convince Republicans.
I don't know if US law has the beyond reasonable doubt/balance of probabilities distinction we have in the UK, or if it does what the standard is for impeachment proceedings. But I think it's a fair guess that it requires evidence that puts things "beyond reasonable doubt" in order to convince enough Republicans. And that doesn't mean transcripts which can (with a following wind and clapping the telescope to one's blind eye) be interpreted as a joke. It means bank transcripts, transactions, unpicking of webs of shell companies. It means leaking of classified information which can be shown to compromise sources and have clear impacts on US national interests.
I think our Trumper visitor in the middle of the night actually served as a useful reality check. At the moment, seen from the Republican end of the telescope, things look as the Clinton e-mail server did to a die-hard Democrat in the run up to the election: stupid things have been done, but there's no proof of actual leaking of classified information as a result, no evidence that it was done with malicious intent, nor evidence of real damage having been done as a result. So viewed from that end of the telescope, there's not enough to swing the Republicans in Senate.
And a rushed and failed impeachment would do more damage to the Democrats at the midterms than a long drawn out investigation which was still rumbling on - because voters would vote on the balance of probabilities, not on things being beyond reasonable doubt.