Sanders is doing exactly what he's been doing throughout his 33 years in Congress: building his own political and commercial brand by hurting Democrats, thereby helping Republicans, knowing full well that he's hurting the people whom he's pretending he wants to help. In this case, Palestinians (and Israelis too).
He's trying to force a vote on his resolution, which provides a political win for Republicans who vote against it, and hurts Democrats no matter how they vote on it.