Donald Trump's pick in the Alabama Republican Senate runoff crashed to defeat on Tuesday against a populist former judge, likely sending shockwaves through establishment Washington and denting the president's influence over his restless political base.
The result is an embarrassing setback for Mr Trump that highlights the deep divisions within his party and raises questions about its future direction as the GOP heads toward mid-term elections in 2018.
It also signals that many in the grassroots conservative movement that helped propel Mr Trump to the White House are still fighting against the party leadership and its grip on Washington politics during a turbulent period in which Republicans have struggled to deliver on key campaign promises like health care reform.
With 65 out of 67 counties reporting, former Alabama state chief justice Roy Moore led incumbent Luther Strange by 54.9 per cent to 45.1 per cent.
Mr Strange was appointed to the US Senate earlier this year to fill the seat vacated by Jeff Sessions, whom Mr Trump picked to be his attorney general.
Mr Moore hailed his win as a "conservative victory" for his state.
"Because of you, tonight, the establishment has been DEFEATED in Alabama!" he posted on Twitter.
Mr Moore now becomes the heavy favorite in Alabama's special election to be held in December against Democratic nominee Doug Jones.
Mr Trump offered his own congratulations to Mr Moore, urging him in a tweet to "WIN in Dec!"
While Mr Trump may be shifting his support to outsider Mr Moore, the race in Alabama, in the heart of the Deep South, was the latest political battleground over the direction that the Republican leadership is taking the party in Washington.
In a political twist, the race was the stage for a proxy war of sorts between Mr Trump and his recently ousted White House chief strategist Steve Bannon, who backed Moore.
Mr Trump appeared at a rally for Mr Strange on the weekend when he unleashed an attack on NFL players who took the knee during the national anthem.
On Friday, he told the crowd: "Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, to say: 'Get that son of a b**** off the field right now, out. He's fired. He's fired!'"
