"A suppressed vote"

Paul Soglin makes a surprising (to me, anyway) claim about Tuesday’s election (emphasis added):

The close outcome, with a suppressed vote, demonstrated that the influence of Wisconsin Manufacturers and Commerce…no longer have a magic bullet that guarantees they can win elections.

I’m far from the most aware member of the Cheddarsphere, so maybe somebody else can clue me in: how was the vote suppressed? And where?

Or is that just his way of saying “low turnout?”