# 1940 United States Senate election in Wyoming

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The 1940 United States Senate election in Wyoming took place on November 5, 1940. Democratic Senator Joseph C. O'Mahoney ran for re-election to a second full term. He faced Republican Milward Simpson, a member of the University of Wyoming Board of Trustees and a former State Representative, in the general election. Though the presidential election in Wyoming was relatively close, O'Mahoney outperformed President Franklin D. Roosevelt, and defeated Simpson in a landslide to win his second term.

## Democratic primary
### Candidates

* Joseph C. O'Mahoney, incumbent U.S. Senator
* Cecil W. Clark, former Weston County Prosecuting Attorney

### Results

Democratic primary :
| Party | Party | Candidate | Votes | % |
| | Democratic | Joseph C. O'Mahoney (inc.) | 25,473 | 90.45% |
| | Democratic | Cecil W. Clark | 2,688 | 9.55% |
| Total votes | Total votes | Total votes | 28,161 | 100.00% |

## Republican primary
### Candidates

* Milward Simpson, member of the University of Wyoming Board of Trustees, former State Representative
* Harry B. Henderson, Jr., State Senator
* Charles E. Winter, former U.S. Congressman
* Irving W. Dinsmore, former State Senator
* R. R. Crow, State Representative

### Results

Republican primary :
| Party | Party | Candidate | Votes | % |
| | Republican | Milward Simpson | 12,014 | 37.47% |
| | Republican | Harry B. Henderson, Jr. | 8,816 | 27.49% |
| | Republican | Charles E. Winter | 6,128 | 19.11% |
| | Republican | Irving W. Dinsmore | 2,910 | 9.08% |
| | Republican | R. R. Crow | 2,197 | 6.85% |
| Total votes | Total votes | Total votes | 32,065 | 100.00% |

## General election
### Results

1940 United States Senate election in Wyoming :
| Party | Party | Candidate | Votes | % | ±% |
| | Democratic | Joseph C. O'Mahoney (inc.) | 65,022 | 58.74% | +2.11% |
| | Republican | Milward Simpson | 45,682 | 41.26% | −1.69% |
| Majority | Majority | Majority | 19,340 | 17.47% | +3.80% |
| Turnout | Turnout | Turnout | 110,704 | | |
| | Democratic hold | Democratic hold | Democratic hold | Democratic hold | Democratic hold |