Dylan Matthews in Vox answers this question, given the Democrats’ Congressional losses under Obama.
“After reviewing the numbers, and talking to some political scientists doing research on related issues, I think pessimists are too pessimistic, but they also have a point. A Democratic recovery is possible, but it’ll take a while.”
“It’s normal for the party in the White House to lose ground elsewhere. That said, as this graphic by Vox’s Sarah Frostenson demonstrates, Obama’s losses in the House are bigger than even those suffered by Republicans under Richard Nixon and Gerald Ford, or by Democrats under Bill Clinton when their decades-long stranglehold over the body finally ended in 1994. Nixon and Ford may have lost more at the state legislature level than Obama, but Obama’s losses dwarf those of any two-term president since.”
“However, governorships and the Senate are a more mixed story, with Clinton posting larger losses:”