Two Democratic presidential primaries are taking place: Kentucky, with 55 pledged delegates up for grabs, and Oregon, with 61 delegates. Kentucky also has five additional superdelegates and Oregon an additional 13, but those are not specifically at stake Tuesday.
For Sanders, erasing Clinton's lead in pledged delegates (currently 1,722 to 1,424) will take winning about two-thirds of those that remain. That's to say nothing of Clinton's huge edge among superdelegates
-- a project Sanders is saving for later.
Kentucky should be a good state for Clinton. Her husband was the last Democrat to carry it in a general election, in 1992 and 1996, and she beat then-Illinois Sen. Barack Obama there in 2008.
In an attempt to avoid her mistakes in Indiana
(where Sanders spent nearly $2 million to Clinton's $0 on the airwaves, and Sanders narrowly won), the Democratic front-runner has invested more time and money in the Bluegrass State.
She's held 11 campaign events over three visits in a two-week span.
"Everybody's ready to go vote," Clinton said in Paducah on Monday. "I'll tell you this: I'm not going to give up on Kentucky in November."
But Clinton's campaigned hard and still lost before -- most notably in Michigan.
Clinton knows that with a big delegate lead, wins in states like Kentucky could turn Sanders' efforts to catch her from improbable to impossible. As soon as she can do that, she can turn her attention fully to presumptive Republican nominee Donald Trump -- a pivot Clinton has wanted to make for two months.
2. Sanders needs to win -- big
Sanders, meanwhile, will have his eyes on Oregon, a culturally liberal West Coast state where he'll need to rack up a massive margin of victory -- and hope it'll foreshadow similar results on June 7 in California.
Since a blowout in Kentucky is unlikely, the Vermont senator will need to crush Clinton out West.
It'll have to start with a win in Oregon. Then, he'll need to pick up smaller states like Montana and North Dakota -- and top it off with a big win in California.
"Here in North Dakota and the remaining seven other states we're going to have to win about 65% of the pledged delegates. Right now were at about 45.5%. I want to be at 50% plus one," he said Friday in Fargo, North Dakota. "So that's task No. 1."
3. How Obama helps Clinton in Kentucky
To understand why Clinton could win Kentucky on Tuesday, consider the state's recent history in gubernatorial elections.
Then-Gov. Steve Beshear, a popular Democrat even in the red state, embraced Obama's Affordable Care Act, and his implementation served as a national model. He's been succeeded by Republican Matt Bevin, who has set out to dismantle everything Beshear built, but also seen his approval ratings decline
Kentucky is a culturally conservative state with a history of electing moderate Democrats to statewide offices. That history -- combined with Clinton campaigning as the protector of the Obama (and Beshear) legacy -- will aid her in a state where bigger liberal programs like Sanders' Medicare-for-all proposal seem especially out of reach.
Another factor working in Clinton's favor: Kentucky is a closed primary, which means only registered Democrats can participate -- not the independents Sanders has so successfully brought into the voting booth elsewhere.
She'll look to run up a significant margin in Jefferson County, home of Louisville and much of Kentucky's African-American population.
4. The GOP race is over
There's nothing to watch on the Republican side on Tuesday.
Sure, Oregon is holding a GOP primary, too. But Ohio Gov. John Kasich -- who less than a month ago struck a deal with Texas Sen. Ted Cruz to get a one-on-one showdown with Donald Trump there -- has already dropped out of the race.
The only question to keep an eye on is whether Oregon Republicans will attempt to sending a message by refusing to vote for Trump.
Still, Oregon is on pace to break the 1 million vote mark for only the second time in its history in a primary -- with 2008, when Obama and Clinton were still competing, being the first.
5. Rand Paul's mistake
It was early 2015, and Kentucky Sen. Rand Paul had a problem: He knew he was running for president -- but he also knew Kentucky state law prohibited from hedging his bets by staying on the ballot for re-election to the Senate, too.
So he came up with an alternative. Paul raised and paid $250,000 to have Kentucky scrap its Republican presidential primary (originally set for Tuesday) in favor of caucuses to be held March 5.
The problem: Paul didn't last even close to long enough to compete in Kentucky's presidential caucuses.
The money was a waste, and now, Paul is on the ballot for a second term in the Senate.
That's why in Kentucky, only Democrats will vote Tuesday.