Here is a list of the 2018 Senate candidates as far as they are current known. The color of each line indicates which party currently holds the seat. An asterisk after a candidate's name indicates that he or she is an incumbent running for reelection.
The map hugely favors the Republicans. Ten Democratic senators are up in states Donald Trump won. Only one Republican is up in a state Hillary Clinton won. Seven Democrats are in states with a Republican PVI (Partisan Voting Index). In addition, Democratic turnout is normally way down in the midterms, giving the Republicans a boost independent of the map.
On the other hand, the president's party is normally whacked badly in the midterms. In 17 of the 20 most recent midterms, the president's party lost seats in the Senate. In short there are factors leaning in all directions, but most of the signs favor the Republicans.
| State | Democrat | Republican | 2012 Results | PVI |
| Arizona | Kyrsten Sinema | Martha McSally | 49% R | R+5 |
| California | Dianne Feinstein* | Kevin de Leon (D) | 63% D | D+12 |
| Connecticut | Chris Murphy* | Matthew Corey | 55% D | D+6 |
| Delaware | Tom Carper* | Rob Arlett | 66% D | D+6 |
| Florida | Bill Nelson* | Rick Scott | 55% D | R+2 |
| Hawaii | Mazie Hirono* | Ron Curtis | 63% D | D+18 |
| Indiana | Joe Donnelly* | Mike Braun | 50% D | R+9 |
| Maine | Angus King* | Eric Brakey | 53% I | D+3 |
| Maryland | Ben Cardin* | Tony Campbell | 55% D | D+12 |
| Massachusetts | Elizabeth Warren* | Geoff Diehl | 54% D | D+12 |
| Michigan | Debbie Stabenow* | John James | 59% D | D+1 |
| Minnesota | Amy Klobuchar* | Jim Newberger | 65% D | D+1 |
| Mississippi | David Baria | Roger Wicker* | 57% R | R+9 |
| Missouri | Claire McCaskill* | Josh Hawley | 55% D | R+9 |
| Montana | Jon Tester* | Matt Rosendale | 49% D | R+11 |
| Nebraska | Jane Reybould | Deb Fischer* | 56% R | R+14 |
| Nevada | Jacky Rosen | Dean Heller* | 46% R | D+1 |
| New Jersey | Bob Menendez* | Bob Hugin | 59% D | D+7 |
| New Mexico | Martin Heinrich* | Mick Rich | 51% D | D+3 |
| New York | Kirsten Gillibrand* | Chele Farley | 72% D | D+11 |
| North Dakota | Heidi Heitkamp* | Kevin Cramer | 50% D | R+16 |
| Ohio | Sherrod Brown* | Jim Renacci | 51% D | R+3 |
| Pennsylvania | Bob Casey* | Lou Barletta | 54% D | EVEN |
| Rhode Island | Sheldon Whitehouse* | Robert Flanders | 64% D | D+10 |
| Tennessee | Phil Bredesen | Marsha Blackburn | 65% R | R+14 |
| Texas | Beto O`Rourke | Ted Cruz* | 57% R | R+8 |
| Utah | Jenny Wilson | Mitt Romney | 65% R | R+20 |
| Vermont | Bernie Sanders* | Brooke Paige | 71% I | D+15 |
| Virginia | Tim Kaine* | Corey Stewart | 53% D | D+1 |
| Washington | Maria Cantwell* | Susan Hutchison | 61% D | D+7 |
| West Virginia | Joe Manchin* | Patrick Morrisey | 61% D | R+20 |
| Wisconsin | Tammy Baldwin* | Leah Vukmir | 51% D | EVEN |
| Wyoming | Gary Trauner | John Barrasso* | 76% R | R+25 |