Nick Lyon becomes highest-ranking official to face criminal charges after two men died from Legionnaires' disease during contaminated water scandal.
Snyder is under pressure to resign over the state's poor handling of a lead water crisis in Flint.
Lawmakers ask Michigan Governor Rick Snyder and Environmental Protection Agency Administrator Gina McCarthy to step down.
The residents allege that officials failed to take action to end the ongoing contamination.
The candidates met Thursday in Detroit, which is 70 miles from the ongoing water crisis in Flint, Michigan.
The emails were sent months before the governor said he learned of the outbreak and the possible reasons behind it.
Susan Hedman's resignation comes as criticism of both the state and federal response to the toxic-water crisis continues to grow.
Drinking water in Flint, Michigan, was contaminated with high levels of lead after the state switched supply sources.
One of Snyder's aides warned the crisis could become "political football."
Anti-abortion campaigners use a rare, veto-proof tactic to turn the clock back on women's health care.