Former Vice President Dick Cheney’s daughter Liz Cheney announced in a video Tuesday that she will challenge Sen. Mike Enzi in Wyoming’s Republican primary race next year, a decision certain to split the state and national parties in what promises to be the most competitive Senate primary ever for a Wyoming Republican incumbent.

“I am running because I believe it is necessary for a new generation of leaders to step up to the plate,” Cheney said. “I am running because I know, as a mother and a patriot, that we can no longer afford simply to go along to get along. We can’t continue business as usual in Washington.”

The decision marked a turnaround for Cheney, who initially appeared hesitant to challenge Enzi even as her father began to contact donors on her behalf. Just last year, she called Enzi “a terrific senator and an old friend.”

“I’m sure he’ll let folks know when he’s ready to let folks know about his decision in 2014,” she said at the time.

Enzi reacted nonchalantly to the news when reporters surrounded him just off the Senate floor, saying Cheney’s announcement would not alter his legislative or political schedule — nor would her entry into the race scare him out. The senator said he returns to Wyoming and travels the state every weekend, and he took a dig at Cheney —until recently a Virginia resident — saying that anyone from the Equality State would know that its residents don’t like long campaigns.

“Nobody in Wyoming likes a long campaign, and anybody from Wyoming would know that,” Enzi said as he stood beside fellow Wyoming Republican Sen. John Barrasso. “They’ll be able to make up their mind in a lot less time than from right now till next August. My job is to be the U.S. Senator that I was elected to be until at least January of 2015. And the people of Wyoming expect me to do the job.”

Barrasso said Cheney is “talented and has a bright future.” But he called Enzi a friend and a mentor, and made clear that he will support his colleague for re-election.

On Twitter, Ari Fleischer, a former press secretary for President George W. Bush, echoed that sentiment.

“I’m a big fan of Liz Cheney,” Fleischer tweeted. “But not in this race.”

The national Republican establishment also immediately affirmed its support for Enzi, including Sen. Jerry Moran, of Kansas, the chairman of the National Republican Senatorial Committee.

Moran said the NRSC, the official campaign arm of the Senate Republican conference, was prepared to back Enzi financially and otherwise in his primary against Cheney. The NRSC’s commitment is somewhat peculiar given its limited financial resources for 2014 , and considering that Wyoming’s Senate seat will go Republican regardless of who is the nominee.

“The primary responsibility of the Senate campaign committee is to make certain that Republican incumbents are re-elected; we’ll do everything we can to make certain that Mike Enzi has the help and support he needs from us,” Moran said. “Mike Enzi’s very popular in Wyoming.”

Moran said neither he nor anyone at the NRSC has been in contact with Cheney.

Enzi might well need the aid of his party should outside groups decide to back Cheney. Enzi’s voting record holds a middling rank among Republicans as tracked by the Club for Growth, which has a history of challenging sitting senators — such as when it backed Sen. Mike Lee in Utah, who unseated Sen. Bob Bennett in 2010, and Richard Mourdock in Indiana, who bested Sen. Richard Lugar in 2012.

Barney Keller, a Club for Growth spokesman, would not comment on Enzi’s voting record. “We are watching the race,” he said.

Should Cheney prove competitive to Enzi, it would set a precedent in Wyoming, where an incumbent Republican has never received less than 70 percent of the primary vote. But Cheney will likely be aided handily by her father, the former vice president, who served for about a decade as Wyoming’s lone House member and is an icon in the state — as well as a formidable fundraiser.