If you think the primaries have dragged on too long you may want to console yourself with the reality that as far a the duration of time is concerned we have yet to reach the halfway mark. There are 65 days remaining until June 7 when California, Montana, New Jersey, New Mexico and South Dakota vote. For all practical purpose the remaining contests are Trump versus No Trump referenda. It is a mathematical impossibility for John Kasich to collect the necessary 1237 delegates needed to win the nomination. For Ted Cruz call it an extremely low probability.
At present only 914 delegates remain and to secure the nomination Cruz needs 772. The Wisconsin primary is listed as winner take all which is something of a misnomer. The winner in each of its 8 congressional districts will take all 3 delegates but of the remaining 18 delegates, 15 will serve at-large. Wisconsin's at-large delegates will be allocated on a winner-take-all basis. The candidate who wins a plurality of the statewide vote will receive all of the state's at-large delegates. In addition, three national party leaders will serve as bound delegates to the Republican National Convention. The RNC delegates will be required to pledge their support to the winner of the state's primary. In a nutshell, winning Wisconsin is not apt to be decisive for either Trump or Cruz but there will be 42 fewer delegates left reducing the outstanding count to 872. At present Cruz has a slight lead so for the sake of argument assume he wins statewide and carries 5 congressional districts. That would give him 33 delegates leaving him needing 739.
Looking forward to April 19, New York, where Trump leads handily, offers 95 delegates proportionally allocated. Each of the 27 congressional districts will award 2 delegates to the first place winner and 1 to second place with the remaining 14 delegates allocated proportionally unless one candidate receives 50% of the vote in which case he would take all. Trump leads in the Real Clear Politics average of polls with 54.5%. One might expect that to tighten but assume Trump does pull 50% and carries 18 congressional districts. He goes home with 50 delegates leaving Kasich and Cruz to divvy up the remaining 45. Kasich is probably stronger than Cruz so give him 30, leaving Cruz with 15 ruing the day he mentioned Trump's New York values. The outstanding delegate pool is reduced to 777 with Cruz needing 724.
Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island vote on April 26 putting 172 delegates on the line. No polling is available for Delaware and Rhode Island but Trump leads substantially in the remaining 3 states. Suppose Trump is having a bad day and only wins 58 delegates while Cruz and Kasich bag 57 each. Cruz would need 667 of the remaining 605 delegates. Under this scenario Trump would have only 856 delegates, needing another 381 to reach the required 1237 but this scenario probably downplays his strength. He would have to win 63% of the remaining delegates but as stated the scenario is exceedingly stingy.
It's doubtful either Cruz or Kasich will fold up their campaigns after April 26 but it's going to be exceedingly hard to court votes when the voters know that only a convention can bestow the nomination on one of the two candidates who could not win it on his own. Can Cruz with a straight face intone, "I am the only candidate who can beat Donald Trump"? Can Kasich spoon feed the voters enough bullshit to convince more than a few to waste a vote on him? After April 26 the only votes that will count are votes for Donald Trump.