Veteran Republican Senator Pat Roberts fought off a Kansas primary challenge by a Tea Party-backed doctor who had promised a "family feud" with his distant relative President Barack Obama if elected, results on Wednesday showed.
Roberts secured 48 percent of the vote and Milton Wolf 41 percent in the four-candidate field, according to final but unofficial results, the Kansas secretary of state said.
Roberts has had a 47-year career in Congress and faced conservative challenger Wolf, who said he wanted to "save the Republic."
Wolf acknowledged a distant family tie to Obama but built his campaign on promises to repeal many of the Democratic president's policies. In an interview with CNN, Wolf promised "the mother of all family feuds to save America," if elected.
In primary battles ahead of November's midterm elections, Roberts' showing marked a victory for an incumbent Republican, a pattern that played out more broadly as voters went to the polls in other U.S. states on Tuesday. Missouri, Michigan and Washington state also held primaries.
In Kansas' 4th Congressional District, incumbent Republican Congressman Mike Pompeo won 63 percent of the vote to beat challenger Todd Tiahrt with 37 percent.
Pompeo, backed by powerful food and agriculture companies, has introduced legislation to nullify state efforts to require labeling on foods made from genetically modified crops.
In Missouri, Republican John "Jay" Ashcroft - whose father, John Ashcroft, was Missouri governor, U.S. attorney general and a U.S. senator - won about 54 percent of the vote in his bid for an open seat in the state senate against attorney Jack Spooner, who carried nearly 36 percent with all precincts reporting.
Five of Missouri's U.S. Representatives face primary challengers but are expected to hold their seats going into November's election.
In the Republican primary in Michigan, Tea Party-backed incumbent Justin Amash, member of a rebel group of U.S. House conservatives known for their resistance to compromise, declared victory over challenger Brian Ellis.
Also in Michigan, U.S. Representative Kerry Bentivolio, a reindeer farmer and Santa Claus impersonator, was defeated by challenger Dave Trott, making Bentivolio the third incumbent Republican congressman to lose in a primary so far this year.
In Washington state's fight to represent the 1st Congressional District, early results in the vote-by-mail race showed Republican Robert Sutherland narrowly beating retired Microsoft engineer Pedro Celis, each with about 15 percent of the vote.
Celis, former chairman of the Republican National Hispanic Assembly, was expected to win the primary easily to face off in November against the incumbent Democrat, U.S. Representative Suzan DelBene.
In the state's 4th District, ex-Washington Redskins football player Clint Didier seemed likely square off against former state agriculture director Dan Newhouse, in a Republican-against-Republican race to succeed retiring 10-term U.S. Congressman Richard "Doc" Hastings.