Mainstream Republicans struggle for strategy to stop Trump's climb

By Doina Chiacu and Megan Cassella WASHINGTON (Reuters) - Mainstream U.S. Republicans struggled for a strategy on Friday to stop their party's presidential front-runner Donald Trump from becoming the nominee for the Nov. 8 election. The country's top elected Republican, House of Representatives Speaker Paul Ryan, said he was not interested in an effort to draft him into the White House race. Party leaders want to block Trump because they worry he would not be able to beat Democratic front-runner