National Tea Party groups were dealt a surprise blow Tuesday night when Rep. James Lankford bested T.W. Shannon outright in the Republican primary for U.S. Senate in Oklahoma, denying the GOP a chance for its second African-American senator.

Anti-establishment Beltway conservative groups such as the Tea Party Patriots and Senate Conservatives Fund had lined up behind Shannon, a half-black, half-Chickasaw politician who had risen to become the youngest-ever speaker of the state House in Sooner State history.

Prominent conservatives including former reality star Sarah Palin and Sen. Ted Cruz also endorsed Shannon, who if elected would have joined Tim Scott of South Carolina as the second black Republican senator and become an important new face for Republican outreach to minority groups.

But all the national attention may have worked against Shannon. Local Tea Party groups viewed his prominent endorsements with suspicion and may have thought Shannon’s out-of-state support would hinder him from being an effective representative for Oklahoma.

“That’s why you could have seen some of these grassroots Tea Party votes swing at the last second towards Lankford—they might have had some concerns about Shannon on the national scale,” a senior Oklahoma GOP political aide said Tuesday night. “Oklahomans are not worried about who is loyal to the Tea Party, who is loyal to the Republican Party—they just want someone who was loyal to their state.”

There were few substantial ideological differences between Lankford and Shannon, so the latter’s defeat will be a blow for the Tea Party groups that supported him but not for conservatives hoping for an Oklahoma senator who will reliably conservative.

Lankford, a red-headed two-term congressman, held an edge against Shannon in polling, but the conventional wisdom was that he would not break the 50 percent mark, forcing a runoff between the two in August.

But Lankford defied expectations. On Monday, even his campaign had predicted only a “chance” that he would win outright. With more than 95 percent of precincts reporting, Lankford held a resounding 57.5 percent to 34.3 percent lead over Shannon.

Part of the surprise win may have been the revelation of an investigation of Shannon’s campaign financing. Just days before the primary election, the Oklahoma County district attorney confirmed to a local news outlet that he was reviewing complaints against the state House speaker of coordinating with outside “dark money groups.”

Frank Keating, the former Republican governor of Oklahoma, called the disclosure of the investigation so close to the primary date “regrettable” and suggested it could dampen support for Shannon at a critical point. (Keating didn’t endorse either candidate.)

Another resounding factor was the role Sen. Tom Coburn played in the race. Although the retiring senator was officially neutral, Lankford’s campaign jumped on Coburn’s comment this month that the congressman was a “man of absolute integrity.” The remark was seen by many in Oklahoma as a subtle nod to Lankford.

Oklahoma pollster Bill Shapard, who has conducted a number of surveys on the race for media outlets, told The Daily Beast that the primary had “turned into a what-would-Tom-Coburn-do election” and that Coburn’s comment was tantamount to choosing a successor for his Senate seat.

“Tom Coburn has exercised a lot more influence on the race than anyone has actually realized,” Shapard said.