Ornery,
That's an interesting example at the end of your post. didn't the Supreme Court just this year say that traffic stops such as that described are unconstitutional, if so Justice White as the sole dissenter in the case you mention may have been correct in that dissent.
In any case taking an exit ramp off a freeway hardly seems like justification for a traffic stop to me, a Democrat, which brings up another point; why is it that Republicans, who reportedly champion smaller government and strict adherence to the Constitution, generally support such police actions or as another example think the government should control a woman's reproductive organs, and Democrats, who supposedly favor big government at the expense of individual liberty, generally see these things as violations of individual rights ?
Edit, the case I was thinking of is Indianapolis vs Edmond decided November 2000, case number 99-1030, if anyone wants to look for it.