Eric Bradner at CNN gives an overview of the Republican Party’s civil war: Donald Trump's march to the White House encountered fierce resistance from his own party Thursday as senior lawmakers hesitated to endorse him, party luminaries said they'd skip his nominating convention and others pondered the potential of a third-party bid. House Speaker Paul Ryan said he's "just not ready" to support Trump, becoming the highest elected Republican official to raise concerns about Trump since he became the party's likely standard-bearer this week.