Answer: Mostly Political campaigning and geographical promises
Explanation: states will swing between parties depending on how much a presidential candidate will campaign in that state. For instance, Trump did a lot of campaigning in 2016 in Florida and turned it red, but in 2012 obama won Florida. As for Geographical promises a state will give electoral votes to the presidential candidate who will promise they will take care of the states best features, for example they will promise North Carolinians protection of their farms.