From Gail Shister's column in the Philadelphia Inquirer:
Former 'West Wing' hottie Rob Lowe begins his six-episode arc on 'Brothers & Sisters' Nov. 19, ABC said yesterday. He'll play conservative Sen. Robert McCallister, an interviewee and potential boyfriend for Calista Flockhart's Kitty...
Exciting, yes? No? Well it should be to Toobworld's True Believers!
See, Robert McCallister was the character in 'Jack & Bobby' who grew up to become the President of the United States... in some other TV dimension.
As with the timeline for the TV show remakes in Earth Prime-Time/Delayed, the life of Robert/Bobby McCallister is not aligned between these two dimensions. Unlike with the remakes, however, that's all that is out of alignment; the rest of the timeline appears to be in synch for the time being. (Bush beat Kerry in 2004 in both dimensions, for example.)
At some point after 2009, however, the timelines do split off into different directions, especially because of the "War Of The Americas" which will occur in the 'Jack & Bobby' timeline.
But at least both Robert McCallisters remain true to their political beliefs: according to a website that details the 'Jack & Bobby' chronology, at some point after 2018:
Bobby comes out of the political closet to his mother...as a Republican. (Date is uncertain. It must have been sometime before he ran for Congress. 1x02 "Better Days")
The fact that he looks to be representing California, rather than Missouri, could be easily splained. Besides the difference in age, perhaps his family moved to California, or he moved on his own after growing up as he made his mark in the world after college.
The only way for this exciting tidbit of Toobworld linkage could go off the rails is if we meet any more members of Senator McCallister's family and find out that he doesn't have a brother named Jack and his mother's name isn't Grace.
And since the producers would clearly like to keep Rob Lowe on the show past his six episode arc commitment, that could very well happen.
But it'll be fun to consider while it lasts.