Historically Trump never would have lasted long in the primaries.Historically the party that doesn't hold the Presidency gains power. The Democrats gained in the House and Senate during the Bush years, then the Republicans gained during Obama's presidency.
For whatever reason Americans tend to vote against the current President's party in down ballot elections.
Right now I think it's best to put aside convention when dealing with politics in the USA.
Especially with the disarray of the Dems. I foresee a lot of internal fighting in the coming days. And a lot of deals by Trump with establishment Republicans to get legislation through.