For mid-term elections, yes, they usually swing against the party in power. The extent to which they swing varies wildly, though, so all we know is that there

For mid-term elections, yes, they usually swing against the party in power. The extent to which they swing varies wildly, though, so all we know is that there likes will be a traditional anti-establishment swing, but the magnitude of it is unknown. However, a special election within the months after a Presidential election should follow the same results, since there hasn't been the time to build the resentment necessary for a significant change in voting patterns. That, however, has not been the case with the Trump presidency.