Donald Trump’s executive order targeting mail-in voting is already being challenged by states, while election experts say it’s dead on arrival. Trump signed an executive order Tuesday requiring the Department of Homeland Security to partner with the Social Security Administration to assemble a list of verified U.S. citizens who are eligible to vote. The order also directs the U.S. Postal Service to bar anyone not included on these lists from receiving a mail-in or absentee ballot. Mail ball...