It's an eight year trend in which the political left has hemorrhaged seats in state legislatures, governorships, the House, the Senate, and the Presidency.
Trump has actually had a fairly strong beginning to his Administration, and has seen his approval rating rise to almost 60%.
Meanwhile, regular everyday Americans are watching as costal liberals are in complete melt down mode, dressing up as vaginas, cannibalizing itself, and throwing a perpetual temper tantrum. And they are disgusted with it.
Many of the 25 Senate seats up for grabs on the Blue side of the aisle are in contested areas, which swung for Trump, who cannot afford to be obstinate and retain their seats. Meanwhile the Republicans only have 8 seats up for grabs, most not in hotly contested states.