Scott Walker

In this April 25, 2015 file photo, Wisconsin Gov. Scott Walker speaks in Waukee, Iowa. Organized labor’s fierce opposition to President Barack Obama’s trade agenda threatens to split the political left and deal a new blow to unions if the president prevails in an upcoming House vote. Unions can ill-afford another high-profile defeat. Industrial states including Michigan, Indiana and Wisconsin have enacted “right-to-work laws” after electing Republican governors and legislative majorities. Walker is now a serious GOP presidential contender after winning major showdowns including a recall election against public-sector unions. (AP Photo/Nati Harnik, File)