It only takes a switch of ONE!
Sheesh, a no brainer.
Actually, I have done the math, and your assessment seems wildly optmistic. How did you arrive at such a figure?
I have set up a simple computer program to simulate the election results, based on assumed probabilities for what I deemed the 7 truly competitive races (SD, MN, NJ, MO, NH, CO, AR). I assumed all other races were won by the incumbent party. I gave the GOP a 50/50 chance to achieve a pickup in each individual race in SD, MN, NJ and MO. I gave the Democrats a 50/50 chance to pickup AR, and a 40/60 chance at picking up each CO and NH.
I then ran the program 10,000 times. The results:
GOP gains 4 seats: 0.82%
GOP gains 3 seats: 5.58%
GOP gains 2 seats: 16.11%
GOP gains 1 seat: 27.33%
Stalemate (neither party gains): 28.08%
Dems gain 1 seat: 16.04%
Dems gain 2 seats: 5.16%
Dems gain 3 seats: 0.88%
This puts the odds of the GOP regaining the Senate at approximately 50%. The odds of the Democrats increasing their majority is only about 22%.
If anyone wildly disagrees with my assumptions, let me know. It's an easy program to run, and I can post results under different scenarios.