Applying your analysis to the 1972 election, we have 98 "natural" Republicans. The 1984 election gives us 97 "natural" Republicans.
You are not accounting, as I carefully and clearly do, for the power of incumbancy. Maine, for example, is leaning towards being a "natural" Democratic state, yet they have 2 GOP senators in Collins and Snowe.
North Dakota is a solid GOP state presidentially, yet Conrad and Dorgan are fairly safe Dems.
The "natural" rule really only applies to open seats, and given the extended careers and 6 years election cycles, the number of open seats is fairly limited. The incumbant, regardless of party and state, usually wins in the Senate. Other than Daschle, I think all the incumbants won in 2004 in the senate if I am not mistaken. -
The Senate, more than any other body, has a vast power of incumbancy, it is very unlikely the Senate will every get all that close to it's "natural" breakout for that reason.
Iowa, for example is very very close at the presidential level. But both Harkin (D) and Grassley (R) are basically bomb proof in their seats. It is difficult to project a scenario short of some truly shocking scandal, where Harkin gets defeated for example.
By contrast, Chaffee in Rhode island is a matter of "when" the seat goes Democratic, not "if". With the exception of an entrenched incumbant, or a truly major scandal, or a very large mismatch between the quality of the Candidates, the Dems should get both seats in Rhode Island.
Similarly, a "generic" GOP candidate will usually beat a "generic" DEm in North Dakota.
The 'safety' that Democrats like Conrad have historically enjoyed has been the conjunction of several interlocking factors:
First, the Democrats have controlled either the Presidency or at least one of the Houses of Congress from 1955 = 2003. Hence, they had the ability to deliver the pork for their constitutents.
Second, until the rise of the 'new' media, most voters in the states involved were largely ignorant of the actions of their Senators/Congressmen (except for highly publicized pork projects).
Third, historically challengers in these jurisdictions have been starved of adequate funding to contest the elections. The money bags in these areas tend to be only interested in tax breaks/subsidies for their interests, and not in other issues. Recently the GOP has developed the ability to provide adequate seed money for candidates without reliance on local money bags.
Fourth, the Republicans have developed a 'turnout' system which is especially critical in off (Presidential) year elections. The Democrats have been relying on the likes of Soros, who can deliver in big city states, but is not effective in rural/small town states.
That being said, I think the GOP may 'blow it' by failing to take effective action on immigration. People do NOT want to have illegals 'legalized,' they want illegal immigration stopped, and illegals expelled (even Hillary Clinton understands this).
