The old South

Fifty years ago, almost all of the senators from the South were Democrats--today, only two (out of twenty-two) are.  But many accounts of the shift suggest that there was little change in political philosophy--it's just a matter of going from conservative Democrats to conservative Republicans.  It's possible to check this using the DW-Nominate scores, which basically try to reduce all roll-call votes to a small number of dimensions.  Although it's not based on prior classification of votes as liberal or conservative, the first dimension generally turns out to be pretty much equivalent to liberal-conservative positions on economic issues: for example, in the 2011-12 session, Bernie Sanders was at one extreme, while Rand Paul was at the other (closely followed by Mike Lee).

Since the scale of the scores doesn't have any natural interpretation, it's easier to work with ranks.  Here is a comparison of the ranks of Southern and non-southern senators on the first dimension in three sessions (1 is most "liberal"):

                   Non-South            South              

2011-12            46                     71

1963-4              50                     60

1947-8              51                     42

Another way to look at it is to divide senators into groups.   Here are the number of Southerners among the 30 most "liberal" and 30 most "conservative"

                      liberal                conservative
2011-12           0                         11
1963-4             4                          5
1947-8             4                          1

So it appears that Southern senators have moved well to the right since 1964.  I'd known that there used to be a some southern liberals, but was surprised that there weren't many consistent conservatives--if ideology were independent of region, you'd expect about 6.5 southerners in the 30 most conservative, so southerners were actually under-represented.

Of course, this comparison is limited to the first dimension--there was also a second dimension corresponding to civil rights issues, and southerners were almost uniformly on the "right."  The major exceptions were Al Gore, Sr. and Ralph Yarborough, both of whom lost their seats in 1970.