The big prize for the two U.S. Democratic Party presidential hopefuls is still three weeks away, but there are four primary contests beforehand that could help decide the race.
Up for grabs are 213 delegates in those four contests ahead of the big California primary, which itself offers 546 delegates.
While former Secretary of State Hillary Clinton leads Vermont Senator Bernie Sanders by nearly 300 pledged delegates going into this Tuesday's primaries in Kentucky and Oregon, Sanders continues to win contests and has pledged to stay in the race until the July party convention in Philadelphia.
With Donald Trump set as the presumptive Republican nominee, Clinton's team would like to turn its attention to the general election contest, but her campaign still can't fully make that shift.
Clinton's delegate total, including so-called superdelegates pledged to support her, is about 50 short of what she would need to clinch the nomination. Sanders is more than 900 short.
A win in at least one of the two contests this week would give Clinton momentum heading into the primaries in California and New Jersey next month.
Oregon is likely to go for Sanders, but Clinton's campaign thinks the race is competitive in Kentucky, where she was spending Sunday and Monday courting voters.
On Sunday, she dropped in at Louisville churches and had two get-out-the-vote rallies on her schedule.
"It will be close, but either way, as with all the contests this month, we will gain additional delegates and move that much closer to clinching the nomination," spokesman Brian Fallon said in an email to reporters.
Clinton has avoided calling on Sanders to drop out of the race. But observers worry that Sanders could damage her chances by staying in.
Meanwhile, Trump adviser Paul Manafort told CNN's State of the Union program Sunday that the campaign is hoping to appeal to Sanders' supporters in the general election.
"You see Democrat support for Bernie Sanders that is potential Trump support, when it's indicated that they will never vote for Hillary Clinton, and when you analyze who those people are that are saying it, they're the very demographic that Trump is appealing to in independents and crossover Democrats," Manafort said.