Cheney, the oldest daughter of former Vice President Dick Cheney, cited "serious health issues" in her family in announcing the end of her campaign against three-term Republican Sen. Mike Enzi.
“Serious health issues have recently arisen in our family, and under the circumstances, I have decided to discontinue my campaign," she said in a statement. "My children and their futures were the motivation for our campaign and their health and well-being will always be my overriding priority."
But her campaign had struggled mightily from the outset. She was trailing Enzi in the polls, battling a reputation as a carpetbagger who had only just moved to the state, and buffeted by a family feud with her over same-sex marriage (her sister Mary Cheney is married to her wife).
CNN first reported Cheney's intention to drop out of the race late Sunday night.
The 69-year-old Enzi is now expected to easily win a fourth term. Wyoming has not elected a Democrat to the Senate since 1970.