When I consider how overt the criminal wrongdoing was in the Watergate breakin, how undeniable the cover-up operation by the administration was--all of it documented by incontrovertible secret tapes--a lot had to "go right" for the House to draw up articles of impeachment. It took over two years from the date of the breakin before Nixon's resignation and it was, by impression, far from inevitable.
It makes me wonder if there are stronger headwinds for Mueller's investigation. Supposing that these two episodes in history are analogous, there are probably no audio recordings of Trump et al admitting plainfully their coordination with Russians or illegal profiteering. Then again, Trump strikes me as incomparably more stupid and sloppy than Nixon, and maybe digital bank records and emails are all the "secret tapes" Mueller needs.