Complex sentence: Due to the closeness of several races, it was initially believed that Senate control would not be decided on election night, especially with Louisiana and Georgia both being competitive and requiring run-off elections if no candidate took a majority of the vote.
Split into simpler sentences: Due to the closeness of several races, it was initially believed that Senate control might not be decided on election night. Both Louisiana and Georgia were seen as competitive, and both states require run-off elections if no candidate takes a majority of the vote.