The violence last night in Chicago that resulted in the cancelation of a Donald Trump campaign rally won't affect the votes of the candidate's most ardent supporters – or opponents. But there are a lot of voters who want to support Trump but aren't sure about him. Then there are voters who lean against supporting Trump but who are persuadable. It is those two classes of voters who could turn this GOP primary campaign on a dime and either give Trump a runaway victory or lead to a loss of support that would hand Ted Cruz a golden opportunity to...