Scratch on insurgent challenge to a sitting GOP senator. Liz Cheney, who has been running against incumbent Republican Wyoming Senator Mike Enzi, is announcing today that she is dropping her bid. Citing "serious health issues" within her family, Liz Cheney announced she is abandoning her challenge to unseat Senator Mike Enzi in Wyoming.

Politico:

"Serious health issues have recently arisen in our family, and under the circumstances, I have decided to discontinue my campaign. My children and their futures were the motivation for our campaign and their health and well-being will always be my overriding priority," Cheney said in the statement.

"Phil and I want to thank the thousands of people in Wyoming and all across the country who have supported my campaign. As a mother and a patriot, I know that the work of defending freedom and protecting liberty must continue for each generation. Though this campaign stops today, my commitment to keep fighting with you and your families for the fundamental values that have made this nation and Wyoming great will never stop."

Late Sunday night, as news that Cheney was likely to drop out of the race swirled, two GOP sources said that a recent incident involving a member of Cheney's immediate family prompted her to reconsider the race, among other factors.

Cheney announced a primary challenge to Enzi last July and raised more than $1 million for her campaign, largely from elite Republicans close to her father, former Vice President Dick Cheney. She has consistently trailed Enzi in public polls.

Before the campaign's conclusion was confirmed, Cheney finance chairwoman Margaret Parry was noncommittal in a short phone call.

"That's a very personal issue, and I think that you need to get a hold of Liz Cheney," she said.

Republicans - including some Cheney supporters - privately expressed surprise at Cheney's move, though she is also said to have been discouraged by Enzi's persistent polling lead and apparent determination to buck pressure to retire.

CNN first reported the news of Cheney's plans.

The departure of Cheney, 47, from the race would clear the way for Enzi, 69, to handily win a fourth term. Wyoming has not elected a Democrat to the Senate since 1970.

Cheney never had much of a realistic shot at beating Enzi. He is very popular in the state, and the GOP establishment resented her challenge. Assuming he wins, Enzi is probably going to retire after this term. Some of the resentment revolves around the question of why Cheney couldn't have waited. There was also the "carpetbagger" problem in that she just moved back to Wyoming in 2012.

That, and the outside money from her father's friends that was fueling her campaign also contributed to the opposition to her candidacy. Then a seriese of gaffes -- including her opposition to her sister's lesbian marriage after apparently being in favor of it -- pretty much proved that Cheney wasn't ready for prime time.