Democrats are calling a last-minute audible on mail-in voting after last night's Supreme Court ruling on Wisconsin.Driving the news: Wisconsin Democrats and the Democratic secretary of state of Michigan are urging voters to return absentee ballots to election clerks’ offices or drop boxes. They are warning that the USPS may not be able to deliver ballots by the Election Day deadline.Why it matters: Supreme Court Justice Brett Kavanaugh was part of a 5-3 majority against allowing Wisconsin to count mail-in ballots that arrive up to six days after Election Day (but were postmarked by Election Day).All ballots must now be received by 8 p.m. on Election Day."Under the U.S. Constitution, the state courts do not have a blank check to rewrite state election laws for federal elections," Kavanaugh wrote.The big picture: More than 66 million people have already voted — roughly 2/3 by mail — putting "this year’s election on pace for a historic rate of participation not seen since the early 1900s," the WashPost reports.Early voting as a share of the total 2016 vote, per the N.Y. Times:Texas: 82%North Carolina: 67%Georgia: 66%Florida: 63%Arizona: 60%Wisconsin: 45%Michigan: 43%Minnesota: 40%Ohio: 39%Pennsylvania: 28%The bottom line: "[T]urnout has surged ... in cities and rural America, in battlegrounds ... and in unexpected places that have not had competitive races in years," WashPost reports."Election Day will feel substantially different from those in past years, with a smaller, more Republican turnout."