I suppose it could go down like this, if we can even make it that far as a country — or planet…
Trump hangs in until the 2018 mid-terms with the help of a spineless majority of House and Senate Republicans who care nothing for the good of the country. Fortunately for the Democrats, the Republicans’ self-destructive caving to Trump’s ignorance and lunacy hands the Democrats a majority in the House, and perhaps the Senate as well. Pelosi becomes Speaker of the House and the Democrats immediately proceed to impeach both Trump and Pence (who will have been implicated in covering up and obstruction of justice throughout the Russia investigation, Flynn escapades, the Comey firing, and probably a dozen more things over the next 18 months). With both President and Vice President guilty of felonies, and if it were possible to eject them both — simultaneously — who would be appointed president? As 3rd in line, would that mean Nancy Pelosi?
Sure, if the Republicans were intelligent they could get rid of both Trump and Pence before 2018 so Ryan could be Prez, but then again, Ryan could be tainted too since he clearly was involved in the whole Nunez - White House attempt at distraction after the first Comey hearing in March.
As perfect as this might sound though, I’m not an expert in the line of succession. I’m also afraid we may not survive that long. Too many days to go. With so much destruction of decades of forward social progress and world order possible between now and the elections in 2018, we can’t afford to wait to take back the house before these two lying turds get flushed.