The opening ad in the Wyoming Senate race, critiquing Liz Cheney for an appearance on MSNBC.

In the political year 2014, the marquee show will be the battle for control of Congress, with Democrats and Republicans each waging tough fights to seize back control of the House and Senate, respectively.

But for sheer pop-some-popcorn-and-sit-back-and-watch entertainment, few contests can measure up to the Republican primary fight in Wyoming, where insurgent Liz Cheney, daughter of the former vice president and longtime state congressman, is bidding to unseat three-term incumbent Sen. Michael B. Enzi.

With little separating the two staunch conservatives on issues, the contest has become a test of personalities and personal connections, celebrity vs. familiarity, and the question of when compromise — like Enzi’s involvement in bipartisan healthcare talks early in the Obama administration — amounts to capitulation.

Now, an outside group is jumping into the contest with the first TV spot of the campaign, a 30-second advertisement that attacks Cheney for, one is led to believe, backing same-sex marriage.

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The spot features clips of Cheney from a 2009 appearance on MSNBC — identified as "the go-to network for Barack Obama and Washington’s liberal elites" — in which she expressed opposition to a constitutional amendment banning the marriage of same-sex couples and support for a State Department move extending benefits to the same-sex partners of Foreign Service employees.

The spot, which ends with the tag line "Wrong for Wyoming," takes a generous share of creative license. Cheney provoked a sisterly spat by declaring in August her opposition to same-sex marriage.

"I am strongly pro-life and I am not pro-gay marriage," Cheney said in a statement issued by her campaign. "I believe the issue of marriage must be decided by the states, and by the people in the states, not by judges and not even by legislators, but by the people themselves."

Her younger sister, Mary, who is gay and married to a longtime partner, responded: "For the record, I love my sister. But she is dead wrong on the marriage issue."

In a small state like Wyoming, where politics is an intimate affair, such a negative spot runs a risk of backfiring, even if it is being broadcast without coordination or consent from the Enzi campaign.The primary dust-up has already divided Republicans and strained both personal and political allegiances inside the state.

Sarah Huckabee Sanders, a spokeswoman for the political action committee behind the spot, American Principles Fund, defended the ad by noting that Cheney said same-sex marriage was an issue best left to individual states. "It’s very clear she doesn’t support a constitutional amendment" banning same-sex marriage, Sanders said. "There’s not one thing she would do to protect traditional marriage at the federal level."

The ad, Sanders said, is set to run for two weeks across Wyoming.

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mark.barabak@latimes.com

Twitter: @markzbarabak