Republican presidential candidates kick off the critical fall campaign season Wednesday night when they take the stage at the Ronald Reagan Presidential Library in Simi Valley, Calif. This would be a good occasion to abandon platitudes and begin hashing out concrete ideas for addressing the nation’s most pressing long-term issue — unsustainable spending on entitlement programs. Any serious plan to get our nation’s fiscal house in order — something that all GOP contenders have promised to do — would have to involve fundamental yet politically controversial reforms of Social Security, Medicare and Medicaid. Over the next decade, those three programs alone will cost taxpayers $21.4 trillion under the Congressional Budget Office’s rosiest scenario. Though commentators often focus on daunting fiscal problems as occurring decades from now, the actual difficulties will hit much sooner, when bond markets conclude that the U.S. has no real plan to clean up its fiscal mess.