it is going to be very difficult to stop Trump. It can be done but it is very very unlikely given the state coming up. States most favorable to Trump are coming up while areas he should of done badly in he did well.
I don't look at it in terms of "easy" or "difficult". I look at it in terms of "what are they willing to risk?" Kasich being in the race means that they will have to risk less. It means that when we come to the convention, it will be 950-Trump 750-Cruz 400 Kasich, 150 Rubio, etc.. instead of 1150 -Trump , 1100 Cruz, 150 Rubio, 50 Kasich, etc...
In the first scenario, they will at least be able to make an argument why it should be someone other than Trump or Cruz.
In the second scenario they will have no argument defending their choice to go with someone other than Trump or Cruz.
I am not suggesting that having an argument or not having an argument will influence whether they do it or not. I think they are going to take the nomination away regardless of any outcome.
The only question now is how costly it will be.
The saddest thing is to watch the lengths they will go to and the jeopardy they will put the party in just to fight Trump or Cruz while they do absolutely nothing to fight Obama.