Following Marco Rubio's loss in his own state, the questions now are: To whom will his supporters turn, and how will his dropping out re-shape the contours of the race?
Kasich's win in his home state is one of the only things standing in the way of a Trump nomination.
Trump must hit the magic number of 1,237 delegates to avoid setting a contested convention into motion.
Florida, Ohio, two Mini Super Tuesday states, and Arizona, which holds its primary on March 22, are the three largest winner-take-all states, with 223 delegates.
In today's voting, Trump still has his eye on big delegate hauls he needs in Illinois and Missouri, where winning several congressional districts can quickly boost his delegate count.
Going forward, Trump will also need a strong performance in New York on April 26, for a total of 95 delegates. While there are no winner-take-all primaries in April and May, he'll need a steady uptick in delegates to reach the 1,237 delegates he needs.
Although Trump will require a large number of wins, he can afford to lose in Nebraska, Montana and South Dakota, which are rural, winner-take-all states that will most likely go to Ted Cruz. The Texas senator also has the edge in the Utah and Wyoming caucuses.
Trump must also win on the final day of GOP voting in California and New Jersey on June 7.
ABC News' Ryan Struyk and Michael Falcone contributed to this report.