What if, in the event of a President's death in the first half of their term, the Vice-President does not serve out the entire remainder of the four-year term but instead only serves until a special election is called to coincide with what would've been the midterm election?
Let's say this is adopted after William Henry Harrison died one month after taking office, once President Tyler was expelled from the Whigs. The new rules state that there will be a new presidential election in November 1842, for which the president will be elected to a four-year term lasting 1843-1847. (So, in other words, the presidential 4-year cycle is now offset by two years.)
Who might the candidates be in an 1842 presidential election, from the Whigs and the Democrats? What might this mean for the annexation of Texas in 1844, and westward expansion afterwards?