The West Wing had an unannounced 1 year jump at some point in season 5 because the writers had trouble coming up with good stories based in the White House and wanted to do a storyline about the next election. That jump doesn't fit in anywhere; if you analyse the fifth season it clearly only takes place over one year, but at the start of season 6 the characters start saying that its their seventh year in office rather than their sixth. The Exec Producer, John Wells, even lied about it in an interview by saying that there was no time jump and that the first season began during Bartlet's second year in office, which just wasn't the case.
I can forgive them because the election story revitalised the show after a relatively poor fifth season, I just wish they hadn't pretended that the jump didn't exist at all.