Sanders is gunning for victory in the Bluegrass State, building on his win last week in neighboring West Virginia as he battles to keep his long-shot nomination bid alive.
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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 given the cold shoulder in the lukewarm recovery from the 2007-2008 financial crisis.
The northwest state of Oregon on Tuesday also holds its Democratic and Republican primaries, where limited polling has indicated Clinton is ahead. Sanders, however, leads in Kentucky.
Clinton sees Kentucky as an opportunity to appeal to a demographic that has consistently snubbed her: working-class white men.
No Democratic presidential candidate has won in the state since 1980 except for her husband Bill Clinton.
On Sunday the former first lady appeared to indicate he would play a role in her administration if she were elected, promising to put him "in charge of revitalizing the economy."
Clinton loses to Sanders in coal state of West Virginia
And during a stop Monday at a diner in Paducah, a city in southwestern Kentucky, she reasserted that he would be her ally in office.
"I've already told my husband that if I'm so fortunate enough to be president and he will be the first gentleman, I'll expect him to go to work... to get incomes rising."
Sanders has also been investing time in Kentucky.
He was in Paducah on Sunday and Bowling Green Monday, holding much bigger rallies -- each more than 2,000 people.
The Clintons have struggled to contain the damage from comments Hillary made in March, when she said she expected to "put a lot of coal companies and coal miners out of business."
She made the comment during a speech on renewable energy but the soundbite stung many in Appalachia.
In Fort Mitchell at the weekend she emphasized her determination to help coal country, saying: "We can't and we must not walk away from them."
Clinton made three stops in Kentucky on Sunday and another four Monday.
"We've got to turn a lot of people out," she told diners in Paducah. "I'll tell you this, I'm not going to give up on Kentucky in November!"
Clinton shook hands, took selfies, offered hugs -- and even chatted with Trump supporters who vowed never to vote for her.
With the Democratic nomination in sight, Clinton is repositioning herself for a bruising general election campaign battle against Trump, the presumptive Republican nominee.
At a later rally in Hopkinsville, Kentucky's secretary of state and close Clinton friend Alison Lundergan Grimes made the succinct case for a steady hand over Trump's unpredictability and the Republican Party's reluctance to unite around their presumptive nominee.
"They have dysfunction. We have a candidate with a plan," Grimes said.
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Clinton used the rally to pummel the "risky and dangerous" Trump, suggesting he is unqualified to handle tough foreign policy decisions.
"I think that we will have in this general election about as clear a contrast as you can imagine when it comes to this issue," she told a crowd of about 500, adding that Trump would be ineffective at the "boring" but important diplomacy that solves crises.
She pointed to her work in late 2012 in helping to defuse sky-high tensions between Israelis and Palestinians, in part by negotiating at length with Egypt's then-president Mohamed Morsi.
"Now ask yourself: how hard would it be for America's secretary of state to negotiate with a Muslim leader if someone running for president -- or heaven forbid were president -- was spending a lot of his time denigrating the religion of the people we had to deal with in a flashpoint region?" she said.
In a November face-off Trump appears destined to hold an advantage over Clinton, at least initially, with working-class whites.
Exit polls in several states have also shown Clinton losing the white male vote by substantial numbers to Sanders.
"She's not trustworthy," Jerry Armaigo, a 68-year-old retiree from the Navy, told AFP at the Paducah diner Clinton visited.
But he acknowledged Trump is not trustworthy either.
In November, "I will vote Republican," he said. "I don't want another four more years of Obama."
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