Harry Enten, writing at FiveThirtyEight.com gives readers the math.
My own delegate estimate has Trump falling short of the 1,237 delegates he needs because he has done poorly in the west so far, and many of those states haven’t voted yet. It’s also possible that Kasich plays better than we might think among moderate voters in the remaining states to vote in New England and Mid-Atlantic.
Moreover, there are plenty of signs that Trump would have lost a majority of states that voted on Tuesday had Rubio not been in the race. I’m talking about Missouri and North Carolina, where Ted Cruz beat Trump in a one-on-one race in the exit polls. Trump may be rising, though he is still not getting close to a majority of the vote in most states. If the anti-Trump voters can find a better way to coordinate behind one candidate, they probably can beat Trump in a lot of upcoming contests.