True, there is a lot of story with her running as an independent. I wouldn't be surprised if they had some scandals pop up like how she is close with the foreign minister of China and countries like Iran. They might have an episode that just deals with the DNC, RNC, and uhhh the independent convention where it's just her and Dalton partying?
We already jumped forward a few weeks at the end of the season to her announcement, I think the next season premiere would probably start out with a bunch of news clips like "Former Secretary of State Elizabeth McCord announces her presidential run, Senator Carlos Morejon announces his run, etc. just to rush through time, maybe to November 2019 or so, then ~1.5 months of time per episode/in between episodes, then that would bring you to Inauguration Day 2021 😛
I think an election night episode would be the second to last episode - they might end an election night episode announcing her win, Conrad coming in and congratulating her, and asking her to sit down at the desk in the oval office, saying something like "You've earned it. Now tomorrow you get to learn what the job really entails"
Then the final episode would be the transition period + inauguration - probably a B plot about a few members of the electoral college disagreeing with McCord being elected and wanting to be faithless electors