US Senator Bernie Sanders scored a decisive victory against Hillary Clinton in the Democratic primary in Oregon, boosting his argument for keeping his underdog campaign alive through the conclusion of the primary process.
Several US television networks on Tuesday called the Pacific northwest state for the liberal Sanders, who was leading the former secretary of state 53 percent to 47 percent.
"Oregon, together we are taking on virtually all of the Democratic establishment. Thank you for the strong victory!" Sanders tweeted after winning the northwest state, known for its diverse landscape of farms, forests, mountains and beaches
But earlier in the night, Clinton claimed victory in an extraordinarily tight race in the state of Kentucky.
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Clinton made the claim ahead of official results. Incomplete results showed her with a narrow lead over Sanders.
"We just won Kentucky! Thanks to everyone who turned out. We're always stronger united," Clinton's campaign wrote on Twitter.
The state board of elections showed Clinton with 46.7 per cent of the vote to Sanders' 46.3 per cent with 99.2 per cent of ballots counted, a margin of less than 2,000 votes.
No US broadcasters have declared a winner in the race, but the Kentucky Secretary of State Alison Lundergan Grimes said on CNN that Clinton looked likely to win the state.
Clinton has a commanding lead in the all-important national delegate count and is marching toward vying for the presidency in the November 8 general election, despite a string of recent primary losses.
Sanders had counted on a Kentucky victory to build on his win last week in neighbouring West Virginia as he battled to keep his long-shot nomination bid alive.
West Virginia and Kentucky are linked to coal, as is much of Appalachia - the largely white, long-struggling eastern US region where many feel they have been left behind in the lukewarm recovery from the 2007-2008 financial crisis.
"We need your help today to win in Oregon and Kentucky," Sanders implored his 2.2 million Twitter followers ahead of the vote, urging them to man phone banks and call voters.
Kentucky held its Republican caucus in March.
Clinton sees Kentucky as an opportunity to appeal to working-class white men - a demographic where the former secretary of state has lagged behind both the celebrity billionaire and Republican frontrunner Donald Trump and Sanders.
John Spenlau, 28, speaking to the AFP news agency outside a voting station in suburban Louisville, said he voted for Sanders because he represented the best hope for "continued change" and the fight against income inequality, among other problems.
"Hillary would be a more stable candidate but I think that Bernie continues to push the envelope, towards a few more of the social programmes that I believe in," Spenlau said.
Clinton, 68, made three stops in Kentucky on Sunday and four more Monday, shaking hands, taking selfies, offering hugs - even chatting with Trump supporters at a smoke-filled diner in the southwestern city of Paducah.
"I will not vote for you. I will never vote for you," disabled veteran Dianna Dooley, 66, told her.
Clinton kept her composure, saying: "That's OK. You vote for whoever you want."
Sanders, 74, invested time in Kentucky as well, campaigning in Paducah on Sunday and Bowling Green on Monday.
But with the Democratic nomination in sight, Clinton is looking beyond the showdown with Sanders to position herself for a bruising campaign battle against Trump.
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At a rally in Hopkinsville, Clinton pummelled the "risky and dangerous" Trump, suggesting he is unqualified to handle tough foreign-policy decisions.
A main "super PAC" supporting Clinton on Monday unveiled a new television ad that skewers Trump for his treatment of women.
The ad, which will air across the crucial swing states of Ohio, Florida, Virginia and Nevada, shows women mouthing Trump's own words, including "you could see there was blood coming out of her wherever", a comment Trump made last year in reference to a debate moderator who asked him tough questions.
Trump shot back Tuesday with criticism that could foreshadow the tone of the coming election battle.
"Amazing that Crooked Hillary can do a hit ad on me concerning women when her husband was the WORST abuser of woman in US political history," Trump tweeted.