Trump's controversial candidacy, propelled by an anti-establishment fervor among Republican primary voters, has caused heartburn for GOP leaders. Some Republican officials have taken the unusual step of denouncing their party's front-runner in the midst of the primary season. Massachusetts Gov. Charlie Baker has vowed not to support Trump, even if he wins the nomination, as have a number of Republican lawmakers on Capitol Hill, including U.S. Rep. Robert Dold of north suburban Kenilworth.