The time jump both does and does not exist. Some time between the fifth and sixth seasons time jumps ahead one year to facilitate the planned election storyline, but there's no possible place in the show where a time jump would fit as the Gaza crisis clearly didn't last a whole year. Towards the end of the fifth season they are preparing for the 2004 midterm elections, yet at the start of the sixth season they are gearing up for the 2006 primaries. It's a massive plot hole, an entire year inexplicably disappeared, but since it prevented another rocky season like the fifth most fans just go along with it.
Exactly. In the season 5 finale Josh is talking to some people about the midterm elections. In the beginning of the 6th season, which is just a few days later, Josh is talking about who should run for president in the next election.
If they planned ahead at all they could have just said season 5 took up two years, however the writers still deny there was ever a whole in the timeline. Even when there clearly is, and when there is the storyline of Toby's brother's death.