The party could be swept at the polls in statewide races for the first time since Reconstruction.
Fourteen have been elected to the senate during the last three cycles.
Three states have no living former members of the upper legislative chamber while six states have just one.
In 2015, Democratic gubernatorial nominees in each of these states received the lowest support recorded by their party in more than 140 years.
Democrats have won just four of 135 elections to statewide office in the Deep South since Barack Obama became president.
The impressive Democratic electoral winning streak in Minnesota is not even the fifth biggest for the party across the country.
It is not a rarity to find a cycle with more than one state hosting elections for both U.S. Senate seats on the autumn ballot.
Eight previous losing Mississippi U.S. Senate candidates, including two U.S. Representatives and two state legislators, have attempted a cumulative 18 comeback bids for the office – losing all 18 times.
Only one region of the country is regularly seeing both parties win U.S. Senate seats in the vast majority of its states.
No appointed US Senator has ever won a primary runoff and only two incumbents who placed second in the initial primary have done so.