The ending is implausible
Spoilers ahead.
At the end of the movie, will Ferrell "wins" the election by 10,000 votes (ballot stuffing is alleged, but they missed an opportunity here of having fun where we could have seen scenes of him punching out scrutineers and screaming at homeless people to vote and vote often!).
At the end, ferrell has a change of heart. So in order to "do the right thing", he suspends his campaign in order to let Zach become congressman.
If that were to happen in real life, will Ferrell would have effectively resigned his seat as a congressman-elect and a new special election would have had to have been called. There is a precedent for this: newt Gingrich resigned his seat in 1998 one day after the midterms because of poor election results. A special election had to be called for his district.