The latest Rasmussen Reports election poll of Washington state's Senate race shows Republican Mike McGavick continuing to chip away at the incumbent's lead. Democratic U.S. Senator Maria Cantwell now leads McGavick 48% to 40%. In March, Cantwell led 49% to 36%. The new poll is the third in a row in which the incumbent has lost a percentage point of support. And it's the second poll in a row showing her at less than 50% support. Meanwhile, McGavick, the former Safeco CEO, has made his strongest showing yet, and is firming up support among Republicans (now 86%) and conservatives (79%)....