According to Charlie Cook, there is only one toss-up House seat in the whole country at this moment. Larry Sabato says there are seven competitive Senate seats--five Republican and two Democratic. This suggests that big Democratic gains are unlikely. Furthermore, Sabato warns that as the perception becomes more widespread that the Democrats will win the White House, it could help Republicans in congressional elections. As he explains:
"In modern times, Americans have often built in an additional check and balance undreamt of by the Founders. They prefer divided party control of the White House and the Congress so that no party holds sway, and the politicians will all oversee and limit one another. Maybe Bush and Iraq are enough to elect Democrats across the board in '08. Or maybe the Democratic edge in the national legislature is a hidden card that the Republican presidential nominee will be able to play in what may be an uphill battle to secure the White House for a third consecutive GOP term."
This is why I think it is important for Republicans to be realistic about their White House chances. If they accept that 2008 isn't their year at the presidential level, they may still be able to salvage something at the congressional level.