As of today, April 15th, 2016, Real Clear Politics (Averages for the past month) has Hillary Clinton beating Donald Trump by 49.0% to 39.1% (a spread of 9.9%) and Ted Cruz by 46.0% to 42.6% (a spread of 3.4%). It also has Bernie Sanders beating Trump by 53.4% to 37.1% (a spread of 16.3%) and Cruz by 50.6% to 39.4% (a spread of 11.2%). Finally, it has John Kasich beating Clinton by 47.3% to 40.6% (a spread of 6.7%) while Sanders beats Kasich by 45.9% to 42.6% (a spread of 3.3%).
If these comparative figures hold through the Republican Convention in the week of July 18th, 2016, three months from now, it would be a Republican death wish for them to nominate Trump or Cruz, anyone but Kasich. Of course, they might make the argument that their guy will destroy Clinton or Sanders in the debates, but how often have debates mattered at all?