Democratic presidential candidate Hillary Clinton speaks at the Union of Carpenters and Millwrights Training Center during a campaign stop in Louisville, Ky., Sunday, May 15, 2016.

Vermont Senator Bernie Sanders and former Secretary of State Hillary Clinton  stressed economic issues as they tried to win over voters in Oregon and Kentucky, who are casting ballots Tuesday in Democratic presidential primaries.

Located almost on opposite sides of the country, the two states are very different but have a similar number of delegates at stake with 74 in Oregon and 61 in Kentucky.

Coal an issue

Sanders easily won last week's primary in West Virginia, a neighbor of Kentucky.  Those states have major coal mining industries and while Clinton has proposed a program to move away from the coal economy into other industries, she has driven away voters who are unhappy with her characterization of putting coal miners out of business.

Democratic presidential candidate Sen. Bernie Sand
Democratic presidential candidate Sen. Bernie Sanders speaks to a gathering of supporters during a campaign rally at the Lexington Convention Center, in Lexington, Ky., May 4, 2016.

The Democratic system of awarding delegates proportionally based on the vote means both Clinton and Sanders will gain delegates as they try to reach the majority 2,383 needed to clinch the party's nomination.  Heading into Tuesday, Clinton has 1,716 and Sanders 1,433 from all of the states that have already held their primary or caucus.

Super Delegates

But hanging over the race are the hundreds of so-called super delegates, who are party officials free to back any candidate.  More than 500 have pledged to support Clinton, while 40 are backing Sanders.  That leaves Clinton needing only about 150 more delegates to clinch the nomination, which she could get by winning as few as 15 percent of those remaining.

Sanders would thus need to win more than 85 percent unless he is successful in his campaign to get the super delegates to switch their allegiance, which they are free to do.  Under an extreme scenario, with all of the super delegates deciding to back Sanders, Clinton could still win the nomination through pledged delegates alone if she won about 35 percent of those still remaining.

Sanders plans to stay in the race through the final voting next month that includes June 7 contests in California and New Jersey. The self-described democratic socialist's message has resonated particularly with young voters who have helped him win 19 states so far.

FILE - A woman blows a kiss to Republican presiden
FILE - A woman blows a kiss to Republican presidential candidate Donald Trump (R) after Trump autographed her chest at his campaign rally in Manassas, Virginia, Dec. 2, 2015.

Trump clinches Republican race

The longevity of the Democratic contest is in contrast to the Republican race, where every candidate except businessman Donald Trump has dropped out, leaving him as the presumptive nominee two months ahead of the party's nominating convention.

After Tuesday, the Democrats have no more contests this month, with only voting in the Virgin Islands and Puerto Rico before the big slates scheduled for June 7.  While the eventual nominee will have to likely wait three more weeks to fully focus on the general election, Clinton and Sanders can take some solace in the multiple polls that show either of them leading Trump in a hypothetical November vote.

Trump has focused his general election criticisms at Clinton, but while he has at times praised Sanders for his campaign against the front-runner, Trump still sometimes goes after Sanders, too.

"If Crooked Hillary Clinton can't close the deal on Crazy Bernie, how is she going to take on China, Russia, ISIS and all of the others?" Trump tweeted last week.