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 | Candidate unknown | 49% R | R+5 |
| California | Dianne Feinstein* | Candidate unknown | 63% D | D+12 |
| Connecticut | Chris Murphy* | Candidate unknown | 55% D | D+6 |
| Delaware | Tom Carper* | Candidate unknown | 66% D | D+6 |
| Florida | Bill Nelson* | Candidate unknown | 55% D | R+2 |
| Hawaii | Mazie Hirono* | Candidate unknown | 63% D | D+18 |
| Indiana | Joe Donnelly* | Candidate unknown | 50% D | R+9 |
| Maine | Angus King* | ACandidate unknownR | 53% I | D+3 |
| Maryland | Ben Cardin* | Candidate unknown | 55% D | D+12 |
| Massachusetts | Elizabeth Warren* | Candidate unknown | 54% D | D+12 |
| Michigan | Debbie Stabenow* | Candidate unknown | 59% D | D+1 |
| Minnesota | Amy Klobuchar* | Candidate unknown | 65% D | D+1 |
| Mississippi | Candidate unknown | Roger Wicker* | 57% R | R+9 |
| Missouri | Claire McCaskill* | Candidate unknown | 55% D | R+9 |
| Montana | Jon Tester* | Candidate unknown | 49% D | R+11 |
| Nebraska | Candidate unknown | Deb Fischer* | 56% R | R+14 |
| Nevada | Jacky Rosen | Dean Heller* | 46% R | D+1 |
| New Jersey | Bob Menendez* | Candidate unknown | 59% D | D+7 |
| New Mexico | Martin Heinrich* | Candidate unknown | 51% D | D+3 |
| New York | Kirsten Gillibrand* | Candidate unknown | 72% D | D+11 |
| North Dakota | Heidi Heitkamp* | Candidate unknown | 50% D | R+16 |
| Ohio | Sherrod Brown* | Candidate unknown | 51% D | R+3 |
| Pennsylvania | Bob Casey* | Candidate unknown | 54% D | EVEN |
| Rhode Island | Sheldon Whitehouse* | Candidate unknown | 64% D | D+10 |
| Tennessee | Phil Bredesen | Candidate unknown | 65% R | R+14 |
| Texas | Candidate unknown | Ted Cruz* | 57% R | R+8 |
| Utah | Candidate unknown | Orrin Hatch* | 65% R | R+20 |
| Vermont | Bernie Sanders* | Candidate unknown | 71% I | D+15 |
| Virginia | Tim Kaine* | Candidate unknown | 53% D | D+1 |
| Washington | Maria Cantwell* | Candidate unknown | 61% D | D+7 |
| West Virginia | Joe Manchin* | Candidate unknown | 61% D | R+20 |
| Wisconsin | Tammy Baldwin* | Candidate unknown | 51% D | EVEN |
| Wyoming | Candidate unknown | John Barrasso* | 76% R | R+25 |