A band of exasperated Republicans — including 2012 presidential nominee Mitt Romney, a handful of veteran consultants and members of the conservative intelligentsia — is actively plotting to draft an independent presidential candidate who could keep Donald Trump from the White House. These GOP figures are commissioning private polling, lining up major funding sources and courting potential contenders, according to interviews with more than a dozen Republicans involved in the discussions. The effort has been sporadic all spring but has intensified significantly in the 10 days since Trump effectively locked up the Republican nomination. Those involved concede that an independent...