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Three-term incumbent Sen. Pat Roberts has defeated his tea party challenger, radiologist Dr. Milton Wolf in the Kansas GOP Senate primary. It was still a tighter than expected outcome in the night's marquee race, with Roberts besting Wolf by about eight points. With 100 percent of precincts reporting, Roberts bested Wolf 48.1 percent to 40.8 percent, according to the Associated Press.

Roberts, 78, served in the House from 1981 to 1997 and has served in the Senate since then. Wolf is a second cousin of President Obama on his mother's side, but is a fierce critic, making his opposition to both the president and the Affordable Care Act a hallmark of his unsuccessful campaign.

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This was one of the last opportunities for the tea party to topple an incumbent senator after a several primaries and millions of dollars in unsuccessfully trying to take down long-serving senators in Kentucky, South Carolina, and most notably in Mississippi.

Wolf, a first-time candidate, consistently hit Roberts for being a creature of Washington who had lost his ties to Kansas and he got support from national tea party groups like the Senate Conservatives Fund, Tea Party Express, and the Madison Project. But, in the end it wasn't enough to knock out the incumbent.

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University of Kansas professor of political science Burdett Loomis says Roberts has "already done a lot of changing," and moving to the right, and "he's returned a lot more to Kansas over the last few months."

In February, the New York Times revealed Roberts may own a home in the Washington, DC suburb of Alexandria, Virginia, but not in his home state. He's continued to make similar residency gaffes on the stump, but none were enough to topple him.

"The Wolf challenge was kind of a wake-up call," Loomis said. "At the same time he's 78 year old and he probably won't seek election again … I think Roberts has done all right, the conventional wisdom hasn't been great, he's made some stumbles. I think a stronger candidate could have done better, there may have been some people in Kansas who regret not running, but he was truly preventative and prevented a stronger candidate from getting in the race earlier on."

In 2012, six-term incumbent Sen. Richard Lugar lost in his primary where residency issues also took center stage and while Loomis said the races were "very similar," Lugar had a "far stronger opponent" and he didn't move to the right as "Roberts has over the last several years."

"I think the residency and age were problems without any question, but Wolf wasn't nearly as strong and whatever steam he may have had was lost with the Facebook (scandal) … he never passed the test of being a truly credible candidate," Loomis said.

He's referring to the Wolf controversy that was also revealed in February when it was uncovered that in 2010, the radiologist posted X-rays of grisly images of fatal injuries to Facebook and cracked jokes about them.

In an interview with ABC News on Monday, Wolf apologized if he had "offended anyone" with the gruesome images.

"We're talking about something years ago that was actually removed years ago," Wolf said. "One of the realities of this is that on the campaign trail, I've had so many people come up to me - other healthcare providers, first responders, police officers, folks in the military. People get that we have to joke about some of these things or it will drive us crazy."

Roberts immediately jumped on the scandal by running statewide television ads highlighting the issue, as well as a state medical board investigation into Wolf's behavior, something that may have helped in the end.

Loomis said tighter than expected results between the two could signal to the Democrat in the race, District Attorney of Shawnee County Chad Taylor, that he could have more of a shot, even though a Democrat hasn't held a U.S. Senate seat since 1932 in this bright red state.

"A lot of Democrats may be looking at this more closely," Loomis said. "They may at least think Sen. Roberts has been wounded enough a general election challenger would be in order."

The tea party has their last opportunity to get a Senate victory later this week when incumbent Sen. Lamar Alexander takes on tea partier State Representative Joe Carr in their primary Thursday. Like this race there is little available polling, but he too looks like he will be safe.

ABC News' Ben Siegel and Caleb Jackson contributed to this report.