Sen. Pat Roberts (R-Kan.) won his closely watched primary on Tuesday, dealing a dispiriting blow to the national tea party movement in one of its final chances this year to unseat a Republican senator.

Roberts defeated radiologist Milton Wolf, a combative conservative newcomer who fashioned himself as an ideological twin of Sen. Ted Cruz (R-Tex.) and vowed to bring dramatic change to the status quo in Washington. The senator will be heavily favored to win a fourth term in November, given his state's rightward tilt.

Full results of Tuesday's primaries

His victory raises the odds that for the first time since 2008, no Republican senator will lose in a primary. With most nominating contests complete, the last major test will come on Thursday in Tennessee, where Sen. Lamar Alexander is heavily favored against state Rep. Joe Carr, an immigration hard-liner running to the senator’s right.

Brian Walsh, a former adviser to the National Republican Senatorial Committee, said Republican primary voters appear to be looking not only for conservative purity but for electability.

“The good news is that the NRSC successfully avoided another reiteration of Christine O'Donnell or Todd Akin this cycle,” Walsh said, referencing two tea party candidates who blew winnable races in 2010 and 2012. “The Republican field of candidates is as strong as it's ever been heading into the fall."​

Democratic officials said Roberts’s red state primary victory signaled little about how the midterm elections might unfold. "This is a party that has long-term problems that their primary fights have only temporarily masked," said Matt Canter, deputy executive director of the Democratic Senatorial Campaign Committee.

The perfect record so far for the party’s incumbents, at least in Senate races, has bolstered GOP hopes of winning control of the upper chamber. Party strategists worried about a repeat of 2012, when tea party candidate Richard Mourdock defeated Sen. Richard G. Lugar of Indiana in the primary but lost in November.

Republicans have no margin for error this year. They need to pick up six seats to win the majority, which Democrats have held since 2007.​

With most precincts reporting, Roberts led Wolf 48 percent to 41 percent. Two other candidates combined for about 11 percent.

Kansas was one of four states where voters went to the polls Tuesday, along with Michigan, Missouri and Washington. Several U.S. House primaries were under scrutiny.

In Michigan, Rep. Kerry Bentivolio (R), a libertarian-leaning congressman, became just the third sitting House member to lose a primary this year. Bentivolio, who has clashed with House GOP leadership, lost by a wide margin to businessman Dave Trott. Another libertarian-leaning Republican, Rep. Justin Amash (Mich.), defeated businessman Brian Ellis, who conceded about two and a half hours after polls closed.

Rep. Mike Pompeo (R-Kan.), in the unusual position of facing a GOP challenger running to his left, defeated former congressman Todd Tiahrt. Tiahrt vigorously defended earmark spending, while Pompeo voiced strong opposition. Meanwhile, Rep. Tim Huelskamp (R-Kan.), a vocal foe of House Speaker John A. Boehner (R-Ohio), defeated challenger Alan LaPolice, a former local schools superintendent.

Wolf, a second cousin of President Obama, was given an early boost in February, when Roberts opened himself up to charges that he lost touch with the state. The New York Times reported that Roberts pays rent to supporters to stay with them when he is in Kansas, instead of living in his own house. Roberts owns a home in Northern Virginia.

But Wolf failed to capitalize. He didn’t win the full faith of national tea party groups. He was badly outraised and outspent by Roberts. Wolf was also hamstrung by a Topeka Capital-Journal report revealing he posted X-ray images of gunshot victims and others on Facebook and cracked jokes about them.

Roberts’s campaign and its allies were upbeat heading into Tuesday. His campaign manager Leroy Towns said the team’s get-out-the-vote effort launched about three weeks ago reached more than 200,000 households. He also sounded confident that TV ads the campaign ran about the X-ray controversy were effective.

“Those are things voters need to know,” said Towns.

Six of the 12 Republican senators up for reelection this year drew notable primary challengers. Most of them fizzled and one fell painfully short.

Senate Minority Leader Mitch McConnell (R-Ky.) and his top deputy, Minority Whip John Cornyn (R-Tex.), routed their opponents. So did Sen. Lindsey O. Graham (R-S.C.), who is known for irking conservatives by working with Democrats.

The tea party’s best hopes were dashed last month in Mississippi, where long-serving Sen. Thad Cochran edged out state Sen. Chris McDaniel, a darling of tea party leaders and their advocacy groups.

Even conservative operatives that backed Wolf said the tea party’s prioritizing of the Mississippi GOP Senate primary earlier this summer made it hard for Wolf to catch fire with grass-roots activists beyond Kansas. Although he was on their radar and endorsed, he never became a cause.

“We got in later than we wanted to be since we were tied into Mississippi for an extra three weeks with the runoff there,” said Kevin Broughton, a spokesman for the Tea Party Patriots Citizens Fund, which spent more than $75,000 in Kansas. “Mississippi threw a monkey wrench into our plans.”

Wolf, with his tint of controversy, also failed to become an outsized, ascendant personality among tea party donors nationwide. His struggles to get beyond the social-media stumbles concerned activists and strategists alike, who wondered if he could become a top-tier contender.

Roberts, 78, was first elected to the Senate in 1996. He served in the House for eight terms before that. The senator ran a cautious campaign, refusing to debate Wolf despite his requests.

Roberts was boosted by his high marks on the scorecards of conservative organizations that rank congressional votes, giving Wolf little fodder. In its annual scorecard released earlier this year, the American Conservative Union gave Roberts an 89 percent conservative rating during the Obama presidency — more than 25 points higher than Cochran during the same period. The Heritage Foundation scores Roberts at 93 percent, near the top of its rating system, although it notes that Roberts’s votes have become more conservative over the past year as the primary has neared.

Support for immigration reform hurt Rep. Eric Cantor (R-Va.), the former House majority leader who stunningly lost to long-shot challenger Dave Brat in June. But conservative critics of some Republicans’ work to pass a path to legalization for undocumented workers said Roberts was able to hold their support — nearly crippling Wolf’s chances of riding GOP anger on immigration to a primary victory.

“In other races where a longtime incumbent has been defeated by a tea party upstart, it’s because the incumbent favored amnesty, but that wasn’t the case here,” said Kansas Secretary of State Kris Kobach, a staunch opponent of giving legal status to illegal immigrants. "Roberts has consistently voted against every amnesty bill while in Congress and that fact takes any potential wind out of Wolf’s sails. It’s the missing element.”

-- Wesley Lowery contributed to this post