Even with affirmative action hiring of minorities, they are usually expected to meet the same requirements for getting tenure as non-minorities are...but I don't know if law schools act the same way.
Maybe if Obama is defeated a major law school will offer him its presidency.
There are a lot of adjuncts who do a fine job for colleges—sometimes they have an expertise that no one on the faculty has and offer an evening course in the subject, or teach a rare language for which there is insufficient interest (or funding) to have a full-time person teaching. Many adjuncts have full-time jobs doing something else.
My experience with law school instructors is that they are practicing specialists, who might occasionally teach a class in their specialty.
Many are women who have left their full time practice to raise a family, and teach to keep up the intellectual “chops.”
Some are those with unsatisfying or unsuccessful practices looking for a change (these folks sometime opt for politics instead, like David Wu).
Instructors and adjuncts often have an ENTIRELY different career than law professors. Law profs are typically those who got top grades in law school, demonstrated unusual academic talents in their approach to the law, and follow the academic path from the beginning.