Americans still trust the Democratic Congress far more than the President on "the major issues facing the country." Congress is so deeply unpopular not because they are investigating or obstructing too much, but because they are investigating and obstructing far too little. Every time "Blue Dog" Democrats and Democratic consultants and mindless, conventional-wisdom-spouting TNR types successfully argue that, especially on national security and war issues, Democrats need to capitulate to Bush lest they be politically harmed, they make Democrats look weaker, more like losers, and more impotent (the opposite of the "strength" they think they are projecting) and dig this political hole further and further.
With a President and a Republican Party this deeply unpopular, the only thing the Democrats could really do to harm themselves is to minimize the distinctions between them and Bush, and fail to take a strong stand against the administration. With very rare exception, that is exactly what they have been doing, and that is why they are held in such low esteem. That, of course, has been the predominant critique of Beltway Democratic insiders for quite some time, but this polling data proves this view rather conclusively.
Not much more to say on this. Rather depressing stuff, because right now, Democrats look like a bunch of pansies.