Postmaster General David Steiner told a congressional panel Wednesday that under President Trump’s mandate requiring states to provide lists of voters who received mailed ballots, the Postal Service won’t deliver ballots in states where officials refuse to comply. Democrats on the Senate Committee on Homeland Security and Governmental Affairs slammed this as unconstitutional, saying that Congress, not the president, has the power to determine how the mail operates. Following Mr. Trump’s executive order directing USPS to begin rulemaking on mail-in and absentee ballot services, the agency proposed rules requiring states to submit lists of voters receiving mail-in or absentee ballots....