Secretary of State Kris Kobach, a Republican who endorsed Roberts during the primary, argued that Democratic nominee Chad Taylor failed to declare that he would be unable to perform the job if elected, a requirement of Kansas law.

Taylor’s withdrawal letter cited that law but didn’t explicitly reference any reason for his decision.

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“The law is quite clear on this,” said Kobach. “Those words have to be given meaning, and that is what we’re doing.”

The decision could undermine efforts to unseat Roberts and potentially rewrite the narrative of the 2014 midterms. It’s certain to anger Democrats, who were hopeful that their candidate’s exit from the race would clear a path for independent Greg Orman to challenge Roberts one on one. Recent polls showed Orman ahead of Roberts in a head-to-head race.

In a statement, Taylor argued he was misled by a senior Kobach aide, Brad Bryant, who convinced him his brief withdrawal letter met the legal requirements to end his campaign. He said he intends to challenge the ruling, although it’s unclear if a challenge would be heard in court or by a state Board of Objections.

“Upon confirming that my letter would remove my name from the ballot, I presented identification, signed the notary ledger, and signed the letter before a Secretary of State employee notarized it,” Taylor said Thursday. “I again confirmed with Mr. Bryant that this notarized letter removed my name from the ballot. He again said ‘Yes.’ My candidacy in this race was terminated yesterday.”

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But Kobach told POLITICO that Bryant “did not tell [Taylor]that his filing was sufficient.”

“Mr. Taylor’s an attorney, and it’s interesting — many other people have complied with this law since it was applied in 1997,” he said. “Mr. Taylor, an attorney, either didn’t read the law or didn’t understand the law.”

He also insisted that politics played no role in keeping Taylor on the ballot — he called it a unanimous agreement among attorneys in his office and in the attorney general’s office and said it would’ve been the same if Taylor were a Republican candidate. He added that any challenge by Democrats must be resolved quickly for the state to print ballots by a Sept. 20 legal deadline.

“They will try to make political hay of this. The law really is clear,” he said.

Kobach’s decision comes a day after Taylor’s abrupt withdrawal, announced minutes before a statutory deadline. The announcement immediately heartened some national Democrats, who know that a Roberts loss would cut into Republicans’ calculus for retaking the Senate — especially since Orman says he’s open to caucusing with either party.

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National Republicans, spooked by Taylor’s withdrawal, responded by taking a more muscular role in Roberts’ campaign. Chris LaCivita, a prominent GOP consultant, has been tapped to help steer the campaign through this uncertain period. The news, first reported by The New York Times, comes as Republicans worry about having to expend resources in a contest once considered safe.

Republicans had been prepared to fight to keep Taylor on the ballot if Kobach had made a different decision, said Clayton Barker, general counsel for the state GOP.

“We’ve never seen something like this,” Barker said.

Taylor’s decision to drop out of the Senate race is still a political mystery, but it came after at least one conversation with an out-of-state Democrat: Missouri Sen. Claire McCaskill. Senate Majority Leader Harry Reid has denied involvement in the decision, but a McCaskill aide confirmed that she talked to Taylor.

“She thinks very highly of him and thinks he has a bright political future. And she knows these decisions are both hard and personal,” the aide said. “But we won’t be going into detail about what they discussed.”

Neither the aide nor officials at the Democratic Senatorial Campaign Committee responded to questions about whether McCaskill lobbied Taylor at the committee’s request.