Rep. Diane Black lost the hotly contested Tennessee GOP gubernatorial primary on Thursday, making her the fifth House Republican this election cycle to lose a primary for statewide office. It's a potentially ominous sign for Republicans as the party fights to hold its majority in Congress this fall. Black, who had been considered the favorite in the race to be the GOP nominee in the Tennessee governor's race, joins a chain of fellow Republican House incumbents in Trump states who lost primary bids for higher offices. Reps. Luke Messer and Todd Rokita both failed to clinch the Republican nomination in Indiana's Senate race. West Virginia Rep. Evan Jenkins lost to state Attorney General Patrick Morrisey in his bid to face Democratic incumbent Sen. Joe Manchin this November. Republican Rep. Raul Labrador lost his gubernatorial primary in Idaho.

Republican Reps. Mark Sanford of South Carolina and Robert Pittenger of North Carolina, meanwhile, both lost their primary re-election bids. Black, who had a shot at becoming Tennessee's first female governor, had forfeited the powerful Budget Committee chair position in the House in her bid for the governorship. "It has been my greatest honor to serve our great state. My campaign for governor came up short, but I will not stop fighting for the conservative cause," Black wrote in a statement after her defeat Thursday. Tweet Tennessee will remain one of 22 states to have never had a female governor. Three other women, two Republicans and one Democrat, were also defeated in the gubernatorial primaries for both parties.

President Donald Trump greets Senate candidate Marsha Blackburn during a rally at Nashville Municipal Auditorium in Nashville, Tennessee, U.S., May 29, 2018. Leah Millis | Reuters

While Black's bid fell short, Marsha Blackburn, her fellow Republican in Congress, did win her primary for statewide office. Blackburn easily won her party's nomination for the U.S. Senate race. She will face Phil Bredesen, a moderate Democratic former governor, in her bid to become the state's first female senator. Black and Blackburn are two of 13 female members of the House who are not running for re-election for their current seats this year, which means there is a deficit to make up before counting overall gains for women in the House this year. Still, women made strides in the nominating process for House seats, with more than 29 percent of the total nominees, and at least 50 percent of the Democratic nominees, being women, according to Gender Watch.