Saying it's time for a new generation of leaders in Washington, Liz Cheney, the daughter of former Vice President Dick Cheney, announced Tuesday she will run against Wyoming's senior U.S. senator in next year's Republican primary.

Cheney is taking on popular Sen. Mike Enzi, who announced almost simultaneously on Tuesday his plans to seek a fourth, six-year term.

Cheney's announcement is a political challenge unlike anything Wyoming has seen for years, maybe decades. Republicans in the state rarely challenge incumbents of their own party in national office. All three members of the state's congressional delegation and all statewide elected officials are Republican.

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Liz Cheney, 46, is the elder of the two Cheney daughters. Married with five children, she was a resident of Virginia until recently. She and her husband bought a home last year in the posh northwest Wyoming community of Jackson Hole.

Asked why voters should oust a powerful incumbent in favor of a rookie, Cheney said seniority isn't necessarily an attribute.

"I think that part of the problem in Washington today is seniority. I think it's time for a new generation, for a new generation to come to the fore. I don't see seniority as a plus, frankly," Cheney told The Associated Press in a telephone interview.

Enzi made his campaign announcement more than six months earlier in the political cycle than he has in the past. He said he would continue to "do the job I was already elected to do."

"Working behind the scenes — this is what I have been doing since I was elected and this is what needs to be done," he said by email through a spokesman.

Enzi immediately won the endorsement of colleagues in the Senate, including the National Republican Senatorial Committee.

"Our support will be there for Mike," said the committee's chairman, Republican Sen. Jerry Moran.

The race promises to be hard-fought. Enzi has had few serious Democratic challengers — much less Republican ones — since he was first elected to the Senate in 1996. He remains well-liked around the state as an affable former shoe salesman and mayor of the coal-mining city of Gillette.

Enzi, 69, takes pride in keeping a lower profile and remaining much less partisan than most of his colleagues. He often refers to his "80-20" rule — that opposing parties usually can agree on 80 percent of the details of any given issue — as a model for Republicans and Democrats to work together.

He handily won re-election in 2008 with more than 75 percent of the vote.

Cheney did not specifically criticize Enzi, but she did present herself as an opponent of President Barack Obama's policies and an advocate for smaller government and lower taxes.

"I think it's time for us to say to ourselves, can we continue to go along to get along in Washington?" she said.

Her interest in the seat has been an open secret for months, dating back at least to last year's purchase of a home in Wilson, a community in Jackson Hole, that was listed for $1.9 million.

She appeared onstage with her father at last year's state Republican Party convention. It was Dick Cheney's first public appearance since he underwent a heart transplant, and father and daughter have been working on a book together.

Since then, Liz Cheney has made frequent appearances at county-level Republican events in virtually every corner of the state. She also has been in the national public eye as a Fox News political commentator.

A Wyoming political veteran, Chris Rothfuss, said her candidacy may be a sign of the divisions that have roiled the national Republican Party for several years, with GOP officeholders being challenged from within their own party if they are seen as too willing to compromise with Democrats.

The Democratic state lawmaker, who lost to Enzi in 2008, said Liz Cheney's challenge reflects "everything that's wrong" with partisanship in national politics.

"Mike's being attacked in this election because he's been traditionally willing to compromise and reach across the aisle in a manner that's unpopular with the partisan culture," he said.

"I would also say that the reason that Liz Cheney is running out of Wyoming rather than what in effect would be her home state of Virginia is because we're basically seen as a much cheaper option in trying to obtain a Senate seat. Obviously, it's an attempt to leverage her name recognition," said Rothfuss, a chemical engineer.

Cheney said Wyoming always has been her home and is where her heart is.

"My sense is, as far the carpetbagger charge, is it's from people who don't want to talk about substance, don't want to talk about the issues," she said in the interview.

The Cheneys are well-established as a family with Wyoming roots — an important qualification for anybody seeking major office in the state. Dick Cheney held the state's lone congressional seat in the 1970s and 1980s before he moved up the political ladder.

While Liz Cheney was born in Madison, Wis., her announcement release pointed out that the Cheney family has roots that go back more than 100 years in Wyoming.

Ahead of Tuesday's announcements, Enzi has refused to be critical of the prospect of a Cheney challenge. He said Liz Cheney earlier told him she would run if he chose not to seek re-election in 2014.

"I'm not going to comment on her," Enzi said. "My job is to do what the people of Wyoming expect me to do."

In a show of unity, he and Sen. John Barrasso, R-Wyo., walked off the Senate floor together Tuesday. Barrasso praised Enzi as his "friend and mentor."

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Cheney's challenge of Enzi promises to make many Wyoming Republicans uncomfortable because they will be forced into choosing between two popular figures.

Former Wyoming Sen. Al Simpson, an often frank and witty observer of state and national politics, said Tuesday he couldn't comment on what the race would mean for the Wyoming Republican Party.

"Right now, I have nothing to say at all except one thing, I deeply care about both of them, and that's all I have to say," said Simpson, a Republican.

Cheney holds a law degree from the University of Chicago and has worked as a lawyer for the State Department and the Agency for International Development.

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