Skewed polls and anonymous betting markets are building up Republicans’ expectations. Donald Trump could use that to challenge the result.The torrent of polls began arriving just a few weeks ago, one after the other, most showing a victory for Donald J. Trump. They stood out amid the hundreds of others indicating a dead heat in the presidential election. But they had something in common: They were commissioned by right-leaning groups with a vested interest in promoting Republican strength. These surveys have had marginal, if any, impact on polling averages, which either do not include the partisan polls or give them...