In 2006, when the Democrats got control of the legislature, is when impeachment became possible. "We can't impeach him once we win a majority, because otherwise we won't win the majority." Brilliant. We're now in "pre-crime" territory here.
I remember when Speaker Pelosi announced that impeachment was off the table in 2007. Was she worried that if she left it on the table, people in 2006 would change how the voted? Was she reassuring voters a year earlier?
I believe I may have caused a short circuit in your thinking by using the phrase "subvert an election." On reflection, a better term would be "overturn an election."
The first Clinton impeachment was, IMO, clearly an attempt by the Republican-controlled Congress to remove a President from office. Not because he'd done something that reached the level where he was a risk to the nation, but because he held the office they felt belonged to their party.
The second Clinton impeachment - a likely occurrence IMO - will be an attempt by the Republican-controlled Congress to remove her from office. Like the previous attempt, they will decide to impeach Clinton,
then set about finding a reason to do so.
The Republican Party, and Congress in particular, have been investigating Bill and Hillary for a generation now. Not because they're trying to serve justice, but because they don't want them in power. They couldn't impeach Obama because (as far as politicians go) he's squeaky clean. Clinton? Not so much. If she wins, it is a safe bet the Committee to Continually Investigate Clinton will convene within minutes after the new Congressional class is sworn in, and the goal of that outfit will be to find something - anything - that they can use to initiate impeachment.