"Critical mass" key to affirmative action case    At the dining
hall, minority students no longer cluster together. Actually,
it's more a high-end food court now, and many tables are racial
mosaics - white, black, Hispanic, Asian.  So is this the
"critical mass" of minority students that U.S. Supreme Court
narrowly endorsed in 2003 as an educational goal important
enough to allow colleges to factor the race of applicants into
admissions decisions?   This time, it's Texas defending the use
of race in admissions, fighting a discrimination lawsuit from
Abigail Fisher, a rejected white applicant. As it happens, the
court's decision will affect relatively few students at Texas,
which admits most students through a system that doesn't factor
in race. But a broad ruling rolling back affirmative action
could be an earthquake at other campuses across the country that
make more use of race, potentially changing the educational
trajectories of millions of students.  For all the wrenching
debates about opportunity and fa