Barack Obama is leading Hillary Clinton 51 percent to 39 percent in Oregon which holds its primary May 20, according to a Rasmussen Reports survey conducted May 1. The margin of error is 3 percent. Rasmussen gives Obama twice the lead reported yesterday in a SurveyUSA poll. On the inevitable question about the Rev. Jeremiah Wright effect, three-quarters of Oregon Democrats say they have been following the story. Forty-four percent say they believe Obama was surprised by Wright’s recent series of public statements, and 34 percent believed Obama issued his latest denunciation out of political expediency, a result that differs from Rasmussen’s national poll, which found that a majority of voters thought Obama’s motives were political, not principled.