The AFL-CIO will endorse Kansas Senate candidate Greg Orman, a spokesman for the labor union tells National Journal, giving the independent candidate from Kansas a last-minute lift in his race against Republican incumbent Pat Roberts.

Orman has been one of the midterm elections' surprise candidates, emerging as a serious threat to defeat Roberts despite the state's conservative electorate. But he's been hindered by a lack of support from outside groups—the Democratic Senatorial Campaign Committee and the Senate Majority PAC, wary of backing a candidate who has said he will caucus with whatever party holds the majority, have declined to help his campaign. Republican-leaning outside groups, meanwhile, have started spending millions of dollars on TV ads in an attempt to salvage Roberts's candidacy.

Just a day earlier, the U.S. Chamber of Commerce—the AFL-CIO's traditional nemesis—announced it would run a new anti-Orman ad campaign worth more than a half-million dollars.

The AFL-CIO won't run TV ads for Orman, spokesman Jeff Hauser said, but his campaign will now be incorporated into the union's extensive ground game there. The AFL-CIO had previously endorsed Kansas's Democratic Party's gubernatorial nominee, Paul Davis, who is locked into one of the country's most competitive gubernatorial contests with incumbent Republican Gov. Sam Brownback.

Hauser says the group is also sending a mailer to 94,000 union members in Kansas, which focuses on questions of Roberts's residency in the state. It features a Wizard-of-Oz-style yellow-brick road leading to the U.S. Capitol, with the words, "Pat Roberts, he's not in Kansas anymore" underneath. The New York Times reported earlier this year that Roberts lives in Northern Virginia most of the year, retaining voting registration in Kansas at the house of a donor. The story plagued him during a difficult primary and left him weakened for the general election.

His vulnerability has been a surprise problem for the GOP and, should he lose, might prevent the party from taking the Senate majority. Republicans have moved aggressively to prevent that from happening, replacing Roberts's chief strategist and campaign manager with a pair of seasoned veterans. And they've assailed Orman, who voted for President Obama in 2008, as just another liberal trying to convince voters he's an independent.

The AFL-CIO's endorsement could help bolster the GOP's case: Labor unions are not popular among  Republicans, and Orman has to win over a lot of Republicans to win in November.

The group's endorsement might also raise eyebrows for another reason: Orman, a wealthy former business executive, doesn't fit the profile of most candidates the AFL-CIO supports. Asked why the group was backing him, Hauser said it was the Kansas AFL-CIO's decision, but pointed to Roberts's lifetime 13 percent on its voter scorecard.

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