The authors' bottom line was a cap that would gradually reduce greenhouse gas emissions, ultimately achieving 80 percent reductions from 1990 levels by 2050. Everything else was negotiable. When Obama entered the fray on May 5, summoning all 36 committee Democrats to the White House, he didn't make a single demand. Rather, participants say, he pointed to a portrait of Abraham Lincoln and said, "He had a chance to affect history. You, too, have a chance to affect history."