Bernie Sanders' presidential campaign has requested a re-canvass in Kentucky's presidential primary, where he trails Hillary Clinton by less than 0.5% of the vote.
The Sanders campaign said it has asked the Kentucky secretary of state to have election officials review electronic voting machines and absentee ballots from last week's primary in each of the state's 120 counties.
Mr Sanders has signed a letter requesting a full and complete check and re-canvass of the Democratic Party's election results in Kentucky.
"He's in this until every last vote is counted and he's fighting for every last delegate," said Mr Sanders' spokesman Michael Briggs.
Mrs Clinton holds a 1,924-vote lead over Mr Sanders out of 454,573 votes cast.
A re-canvass is not a recount but a review of the voting totals. It is unlikely to affect the final outcome but could affect the awarding of a single delegate still up for grabs.
Mr Sanders has vowed to amass as many delegates as possible in his lengthy primary fight against Mrs Clinton, where he trails the former secretary of state by 274 pledged delegates according to a count by The Associated Press.
Mrs Clinton holds a substantial lead with party leaders and elected officials, called superdelegates, and is on track to clinch the nomination through the combination of pledged delegates and superdelegates after contests on June 7.
Mr Sanders can ask a judge to order a recount or an examination of individual ballots but his campaign would have to pay for it.
Mrs Clinton and Mr Sanders both picked up 27 delegates in Kentucky and one remaining delegate will be allocated in the sixth congressional district, which includes Frankfort and Lexington. The delegate will be awarded based on final vote tallies and Mrs Clinton currently leads Mr Sanders by a slim margin of about 500 votes in that district.
The re-canvass is conducted by the state at no cost to the campaign.
A tip in the state-wide vote in Mr Sanders' favour would not guarantee him that last delegate. But if a re-canvass were to determine he actually received more votes than Mrs Clinton in the sixth congressional district, Mr Sanders could earn the last remaining delegate that Mrs Clinton would otherwise receive.
Earlier this year, Mr Sanders could have pressed for a review of voting results in the lead-off Iowa caucuses and in Missouri's primary. He narrowly lost both contests. But in those cases he chose not to contest the results but pursue delegates later in the process.
We must think bigger and bolder to deliver the kind of social transformation we're all demanding.https://t.co/fC4vJ4fbbH— Bernie Sanders (@BernieSanders) May 24, 2016