Ezra Klein has a few:
Can the federal government set the private sector's minimum wage? Can it tell private businesses not to hire illegal immigrants? Can it tell oil companies what safety systems to build into an offshore drilling platform? Can it tell toy companies to test for lead? Can it tell liquor stores not to sell to minors? These are the sort of questions that Paul needs to be asked now, because the issue is not "area politician believes kooky but harmless thing." It's "area politician espouses extremist philosophy on issue he will be voting on constantly."