The problem here is the "historical" premise - the actual numbers don't support using an average. Not only did the 2002 and 2004 elections thwart the expectations of "history," but the "sixth year" average is heavily skewed by elections more than three decades ago.
Since World War II, the party out of power has picked up an average of 34 House and five Senate seats in a president’s sixth year in office...
Democrats should be able to make gains in 2006 based simply on history. But for now, significant gains seem out of reach because they’re trying to fight something with nothing.
Since the end of World War II, there have only been 3 sixth year elections - 1958, 1986, and 1998. (The other three possibilities don't fit - 1950 was Truman's fifth year and his party's eighteenth, 1966 was LBJ's third year and his party's sixth, and Nixon resigned before the 1974 election . Kondracke, oddly enough, seems to be using all of these except 1986.)
Here's the data:
Considering only the likely comparable elections, we're down to a uselessly small sample size of three and 1958 sticks out like a sore thumb. Even considering the other potential "sixth year" elections, there have not been results like this in over thirty years and the two most recent sixth year elections suggest a much smaller change.
The current party split is 55-44-1 in the Senate and 231-202-1 in the House.
Losses for the Party in Power:
Year Senate House 1950 6 29 1958 13 48 1966 4 47 1974 5 48 1986 8 5 1998 0 -4 Average 6 29
Real Sixth Year Losses
Year Senate House 1958 13 48 1986 8 5 1998 0 -4 Average 7 16
A mathematical projection based on these three elections shows Republicans gaining seven seats in the Senate and seven in the House. A gain of seven Senate seats is directly in line with the fact that 62 Senators come from states that voted for President Bush in 2004. President Bush also carried 255 congressional districts in 2004, including 41 represented by Democrats (versus 18 Kerry-GOP districts, a net GOP lead of 23).
Larry Sabato puts it well:
Never in modern times has a president been able to add Senate seats in the dreaded sixth-year election. Of course, look at George W. Bush's remarkable electoral record so far. Sooner or later, there's always a first time for every mark in the record book.There's much more to an election than a batch of shoddy number-crunching. A filibuster-proof Republican majority remains entirely possible.