The split decision amounted to a reassertion of centrism.
"Centrism" is midway between the political right and left, or between conservatism and liberalism. It means that extremism on either side has been rejected by the election. A "split decision" means that the election wasn't very strongly in favor of either side.
Merriam-Webster "split decision"
a decision in a boxing match reflecting a division of opinion among the referee and judges