NASHVILLE, Tenn. — More than five years after U.S. governors began a bipartisan effort to set new standards in American schools, the Common Core initiative has morphed into a political tempest fueling division among Republicans.

The U.S. Chamber of Commerce leads establishment voices — such as possible presidential contender Jeb Bush — who hail the standards as a way to improve student performance and, over the long term, competitiveness of American workers.