Tennessee Primary: Trump-supporting Diane Black, endorsed by Mike Pence, loses to Bill Lee in governor's race

Diane Black, the long-time favourite in Tennessee's Republican primary for governor who was being supported by Mike Pence, has lost to Nashville businessman Bill Lee.

Every candidate in the primary was an ally of Donald Trump — but just one had an endorsement from the White House. Ms Black aligned herself with the president as closely as possible. She ran on a campaign of "Making America great again" and supporting the White House administration’s economic agenda — although she never received an endorsement from Mr Trump himself.

Meanwhile, Mr Lee's campaign was reflective of Mr Trump’s bid for the Oval Office in 2016.

The cattle farmer and business executive is a political newcomer with no experience holding elected office, much like the president. His lack of a track record allowed him to largely avoid heavy criticism from his opponents, until he began leading in the polls near the final stretch of the race.

Mr Lee, who won with nearly 36.7 per cent of the primary vote, will run against Karl Dean, the Democratic former mayor of Nashville, in the Tennessee midterm elections.

The president officially endorsed Mr Lee the day after his primary victory, writing on Twitter, "Congratulations to Bill Lee of Tennessee on his big primary win for Governor last night. He ran a great campaign and now will finish off the job in November. Bill has my total and enthusiastic Endorsement!"

Ms Black’s loss doesn't necessarily indicate that a White House endorsement is no longer powerful in local elections — in fact, it may actually prove the importance of receiving the president’s support.

The former representative’s campaign was dealt a major blow when Mr Trump failed to provide a direct endorsement. Speaking at a campaign speech for Tennessee Republican Senate candidate Marsha Blackburn, Mr Trump said Ms Black was "in a big race."

"Good luck, Diane," he added, without mentioning her again at any point throughout the rally.

Mr Trump is planning to aggressively campaign across the country for conservative candidates in Senate, congressional and gubernatorial races.

However, it remains unclear whether a personal endorsement from the president can secure a victory for firebrand conservatives. Ms Blackburn now faces a close race against Phil Bredesen, Tennessee’s former Democratic governor.

Mr Bredesen sailed to victory on Thursday night in Tennessee’s Democratic primary, and is seen as a moderate who could potentially threaten a Republican stronghold in the state that voted over 60 per cent for Mr Trump in 2016.