The party is hoping to regain seats it lost during the Obama years. Democrats say there are already signs of change, but Republicans argue there's no proof of that yet.
As voters head to the polls in Connecticut, Delaware and Washington, Democrats are hoping to ride some voters' discontent with President Trump to victory.
In state capitals around the country, lawmakers are trying to block voter-approved policies. Critics say it's "lawlessness" that represents the new political climate.