WASHINGTON — President Barack Obama called Democrats and Republicans to the White House today to discuss election-year standoff over the vacancy on the Supreme Court. Neither side showed signs of budging.In an awkward Oval Office sit-down that lasted less than an hour, Senate Majority Leader Mitch McConnell, R-Ky., and Judiciary Committee Chairman Chuck Grassley, R-Iowa, delivered their case for refusing to consider any nominee to the highest court during the throes of a presidential election.Their Democratic …