Re the Presidential timeline-Owen Lassiter was Bartlett's predecessor, 1991-1999. Jimmy Carter and Ronald Reagan were both President in this universe. Newman followed Reagan after a special election that resulted in the West Wing's Presidential election schedule.
On Alternatehistory.com's West Wing timeline, Santos served one tern and was defeated by GlennAllen Walken, who served two terms from 2011-2019. He in turn was followed by none other than Sam Seaborn, who is now running for his 2nd term.