Based on historical results, DG is correct; but hopefully, the people have had enough of the Dems, will avoid the snake oil the 3rd parties are selling, and will vote GOP. It's hard for anyone to predict it this far out anyway; so DG is just guessing at this point.....
The House is almost certainly going to remain in GOP hands, and the majority is likely to increase.
Redistricting has generally favored Republicans, the economy looks to be on a strong rebound by November, and Dubya is doing a great job.
None of those are in the Democrats' favor.