Here's what I would've thought.
2016:
Hillary Clinton runs and picks respected Florida senator Bill Nelson as her running mate. Republicans nominate former Virginia governor Bob McDonnell who chooses New Hampshire senator Kelly Ayotte as his running mate.
Republicans end up flipping VA, CO and NH from 2012 but it's not enough. 306-232 Clinton.
2020:
Hillary Clinton and Bill Nelson both run again. Republicans picked Kelly Ayotte and she chooses Pennsylvania senator Pat Toomey as her running mate.
The GOP flips IA, OH, PA, FL and ME-02 from 2016 making it 306-232.