The dems maybe could get the house if Trump fucks up enough. If only 35 million GOP voters turn out, but 45 million dems turn out (assuming a baseline of 40 million on each side) in 2018 then that would sweep the house even with gerrymandering.
However I don’t think they’d impeach Pence. Trump maybe.
In 2018, it’s impossible, because there’s no way there’d be enough senators on board to remove Pence from office, especially with a Democrat next in line. Trump to Pence, sure, that’s possible, but that’s just because, first, Trump is a lot more reprehensible, and second, because Pence is still a Republican.
And in 2020, it’s moot. It could just maybe possibly become possible to impeach both of them after the 2020 election, but a long time before that would happen, the Democratic candidate for President would win anyway.
He can nominate a VP, but his choice has to be confirmed by both the House and the Senate. If Congress wants the Speaker to take over, they simply don’t confirm the nominee. They can decline to hold hearings (as with Obama’s Supreme Court nominee), stretch out the process indefinitely, or simply vote the nominee down. Easy peasy. That is, if their goal is to make the Speaker the President.
And it also risks having the House flip back to Republican control in the next election. The GOP got very lucky with their SCOTUS nominee strategy. Very lucky. So I guess the question they have to ask themselves is: Do you feel lucky? DO YOU??