"And so, in the most searing and drastic defection of this wild campaign season, [Paul] Ryan broke ranks with the brash New York billionaire. The decision will shape Ryan's political future in the short and long term, and could have a real effect on the outcome of the 2016 election. Immediately, the move could give the 200-plus Republicans up for reelection — particularly those in the swing districts that will decide the size of the GOP's majority, or even whether it keeps the House — a measure of cover from Trump's unpopularity. Many of them think the presumptive nominee is too politically crude to represent the party. Ryan's move came just hours after Trump tweeted 'I love Hispanics!' along with a picture of him eating a taco bowl, not exactly the kind of fence-mending with a growing voting bloc that GOP brass had in mind for Trump's general election pivot. But Ryan's decision to buck the nominee-in-waiting was borne out of opposition to Trump's principles, not any particular policy, according to a source familiar with his thinking...."
From "How Ryan decided to ditch Trump/The speaker did not expect Trump to clinch the nomination so soon and huddled quickly with advisers to plot his break," in Politico.