Fifteen states are left in the battle to collect delegates and 1,237 delegates are needed to clinch the Republican nomination.
The count in the Republican primaries as of Monday looks like this:
Donald Trump leads with 845 delegates; Ted Cruz stands at 559 delegates; and John Kasich has 148 delegates.
A series of northeastern states are next in the primaries on Tuesday. Those states are Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island.
Cruz and Kasich have announced they will work together to try to block Trump from securing the nomination.
But for Trump, it could all come down to California, where there are 93 delegates up for grabs.