Donald Trump’s private meeting Thursday with Senate Republicans — designed to foster greater party unity ahead of the national convention in Cleveland — grew combative as the presumptive presidential nominee admonished three senators who have been critical of his candidacy and predicted they would lose their reelection bids, according to two Republican officials with direct knowledge of the exchanges. Trump’s most tense exchange was with Sen. Jeff Flake (R-Ariz.), who has been vocal in his concerns about the business mogul’s candidacy, especially his rhetoric and policies on immigration that the senator argues alienate many Latino voters and others in Arizona....