And for the first time on the Republican side, there's only one candidate in the race
-- but that doesn't mean there's consensus. Republicans in West Virginia and Nebraska will offer the first glimpse at whether the GOP can rally behind Donald Trump
in a general election.
For Democrats, only West Virginia offers binding results. In Nebraska, Democrats caucused in early March, favoring Sanders by nearly 15 points
. Though Democrats will still be voting in a primary on Tuesday, the results for the presidential race will have no binding effect on delegate allocation.
Do Clinton's coal comments hurt?
Though Clinton won West Virginia over Barack Obama in 2008, she has been in far more hostile territory this time around after comments she made about putting coal miners "out of business."
In a March town hall on CNN, Clinton said her policies would "put a lot of coal miners and coal companies
out of business," continuing to say she was putting forth plans to help those people.
But her critics on the left and right have seized on the remarks, with Sanders campaigning in West Virginia on taking care of coal workers and Donald Trump bringing up her remarks in rallies in the state.
Clinton has tried to walk back the comments, answering emotional questions from voters as she campaigns through the Mountain State. And she has the support of Democratic Sen. Joe Manchin, who told West Virginia MetroNews
last week that he's been talking to her about improving on President Barack Obama's policies in regards to coal.
But in the heavily coal-reliant West Virginia, the damage may have been done.
Does Sanders pick up momentum?
West Virginia is considered favorable territory for Bernie Sanders.
The electorate in the last presidential Democratic primary was overwhelmingly white and working class. The state also has a primary that allows unaffiliated voters to cast ballots in either contest, meaning Sanders can turn out independents. Both of those factors have tended to favor him in past contests.
Though Nebraska's results are non-binding, if the electorate resembles the pro-Sanders crowd in March, he'll have another result to tout on what could be a rough night for Clinton.
Based on CNN's current delegate estimate, Sanders can't overtake Clinton for the nomination with the remaining pledged delegates up for grabs. He would need superdelegates to switch their allegiance
to him from Clinton and pick up pledged delegates in remaining primaries in droves.
The proportional allocation rules in the Democratic primary won't help Sanders catch Clinton -- but he could spend the next month delivering some embarrassing losses to Clinton in states favorable to his campaign.
Will Republicans cast a protest vote?
Trump may be the only GOP candidate with an active campaign, but he won't be the only candidate on the ballot in either state on Tuesday. Both West Virginia and Nebraska will have candidates who have dropped out of the race on the ballot, giving voters a chance to cast protest ballots against Trump should they choose.
Candidates with suspended campaigns have picked up a handful of votes in states after they left the race, but never in large margins. Tuesday will test whether the discomfort with Trump as the GOP nominee can drive voters to the polls to vote against the mogul.
Nebraska will be an especially interesting test case. It's the home to Republican Sen. Ben Sasse, who wrote a lengthy Facebook post
last week arguing for an alternative to Trump for Republicans
who don't want to vote for Democratic front-runner Hillary Clinton. Sasse won his Senate seat in 2014 with 65% of the vote
But Trump also picked up the endorsement of Nebraska Gov. Pete Ricketts
last week even as the rest of the Ricketts family continues to donate to anti-Trump efforts.
In West Virginia, in addition to casting ballots for Trump, voters will also select individual delegates to go to the convention. Delegate hopefuls will be marked with their chosen candidate or as uncommitted when voters make up their minds. To be sure, the Trump campaign in West Virginia sent supporters on Monday a guide to which delegates to select.
Can Trump mend fences with women?
One key statistic Donald Trump's campaign will be watching in exit polling is his standing with women.
Trump has been viewed unfavorably by upwards of two-thirds of women in general election polling, but has done marginally better with women in the Republican electorate. He won 47% of women in the Indiana primary last week, according to exit polls. But he won 59% of men. His chances in November will improve should he be able to close that gender gap.
Democrats have been hammering Trump with some of his comments about women, trying to continue to keep those unfavorables high among the key voting demographic.
Without alternative Republicans in the race, Trump's returns among women could be telling.
Both sides are hoping that a Trump-Clinton matchup could dramatically shift the electoral map
as it has been known since 2000.
Republicans hope that Trump could put Rust Belt states like Ohio, Pennsylvania and Michigan in play for the party.
Democrats, on the other hand, hope that rising demographic trends in states like Arizona, North Carolina and Georgia coupled with Trump's inflammatory statements about minorities could give Democrats an edge in states they have traditionally lost.
With Trump and Clinton holding tight grips on their party's nominations, Tuesday will begin to show signs of what the general electorate could look like, and what issues are motivating them to the polls.