Answers will resolve YES if a majority of seats in the chamber are held by candidates who clearly are primarily affiliated with the Democratic Party.

Fine print:

1. The democratic party must have an actual majority of seats; if chamber is tied but the Democrats have control due to a tie-breaker the answer still resolves NO

2. A candidate may still count as a Democrat even if they are listed on the ballot as an independent (or with no party affiliation), so long as they clearly describe themselves as a Democrat elsewhere.

I've excluded Puerto Rico and American Samoa as to my knowledge the Democrats do not directly contest legislative elections there.