Sens. John McCain and Marco Rubio are poised to win primaries Tuesday as the Republican establishment rallies to defend its embattled members against Donald Trump-style insurgents, setting up Election Day tests that could determine whether the party keeps control of the Senate. “They can try, with difficulty, to chart a middle path between outright rejection or outright embrace of Trump,” said Geoffrey Skelley, of UVA’’s Center for Politics. “Both McCain and Rubio are running well ahead of Trump at the moment. Given the decline of split-ticket voting in recent yea...