According to
210towin.com the 2020 Senate breaks down like this.
Democrat seats not up for re-election in 2020 - 33
Republican seats not up for re-election in 2020 - 31
Democrat seats that are safe in 2020 - 6
Delaware Chris Coons
Illinois Dick Durbin
Massachusetts Ed Markey
New Jersey Cory Booker
Oregon Jim Merkley
Rhode Island Jack Reed
Republican seats that are safe in 2020 (10)
Alaska Dan Sullivan
Arkansas Tom Cotton
Idaho Jim Risch
Louisiana Bill Cassidy
Nebraska Ben Sasse
Oklahoma Jim Inhofe
South Carolina Lindsey Graham
South Dakota Mike Rounds
West Virginia Shelley Capito
Wyoming Mike Enzi - not running for re-election
-
Democrat seats that could be contested in 2020 - 6
Alabama Doug Jones
Michigan Gary Peters
Minnesota Tina Smith
New Hampshire Jeanne Shaheen
New Mexico Tom Udall - not running for re-election
Virginia Mark Warner
Republican seats that may be contested in 2020 - 12
Arizona Martha McSalley
Colorado Cory Gardner
Georgia David Perdue
Iowa Joni Ernst
Kansas Pat Roberts - not running for re-election
Kentucky Mitch McConnell
Maine Susan Collins
Mississippi Cindy Hyde-Smith
Montana Steve Daines
North Carolina Thom Tillis
Tennessee Lamar Alexander - not running for re-election
Texas John Cornyn