Trump never focused his cannons on Kasich. So far when Trump has, Rubio, Bush, Now Cruz, they immediate begin to drop. Hope in California, Cruz popularity will be so blown, that Trump can make quick work of Kasich.
Just nitpicking, I think your remark is generally correct. IIRC, he did in Ohio, and he still fires an occassional shot at the governor. But Trump tends to focus on one opponent at a time, and that is the one who is closest in the contest.