SPRINGFIELD, Ill. — On a late summer afternoon at the Illinois State Fairgrounds, hundreds of Democrats sipped cold beer from clear plastic “JB” party cups as they waited under a large tent to hear their governor’s fiery populist attacks on President Donald Trump’s agenda.

Cutting a broad figure in a casual short-sleeved button-down, Jay Robert “JB” Pritzker, 60, thundered from the stage about Medicaid, Medicare, voting rights, civil rights and food assistance, accusing Trump and his party of demolishing the social safety net.