Democratic and Republican voters will cast their primary ballots in five states -- Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island -- where the respective front-runners hold solid leads.
Democrats are competing for 384 delegates in today's five primaries, while Republicans have 172 delegates up for grabs.
The primaries could bring a sweep for Donald Trump -- but his Republican rivals are already looking ahead, with a strategy aimed at dividing up some of the anti-Trump vote.
John Kasich told NBC's "Today" show that even though he won't be campaigning in Indiana -- where he's giving Ted Cruz a clear path -- he's active in other states, and "will be at the convention."
Bernie Sanders says his campaign is "handicapped" today because the five states don't allow independents to take part. But he tells ABC's "Good Morning America" that he's going to "fight through California and then we'll see what happens."
(CBS News, The Associated Press contributed to this report.)
