It’s not a great time to be the head of an American arts organization, but Kathy Halbreich is thriving at the helm of Minneapolis’s Walker Art Center. The Walker, already one of the Twin Cities’ most popular cultural destinations, is embarking on a massive expansion at a time when other museums are having to scale back, and Halbreich is determined to prove that contemporary art can be a cultural centerpiece even in the dumbed-down world of 21st-century America. “I believe that if the Mall of America is about the consumption of things, a cultural institution like the Walker — if it is properly designed and programmed and inviting enough — can be about the consumption of ideas.”