But it doesn’t necessarily mean that the Democrats will benefit. From “No wonder voters doubtful about Dems” by Thomas Bray on Real Clear Politics:
Democrats hope that George Bush's miserable poll numbers will help them reclaim control of Congress this fall. But polls also show that the Democratic Party's overall approval ratings are almost as deep in the tank as the Republican rating. Voters may be expressing dismay at the alternatives.The closer we get to election day, the greater the chance of a “Paul Wellstone” moment where the Democrats drop the mask and reveal their true agenda.