Before the sun rose on a cold Wednesday morning in January 2019, Fidel Marquez agreed to a life-altering assignment as a cooperating witness in a criminal case the government was building against his colleagues at electric utility Commonwealth Edison and powerful Illinois House Speaker Michael Madigan.

Seizing on a tactic strengthened by a recent U.S. Supreme Court decision, defense attorneys in the Michael Madigan corruption trial began their cross-examination of a key witness Tuesday by trying to distinguish between exchanging jobs for official actions and simply currying favor with the formidable ex-House speaker.