Michigan as a microcosm: Will polling avoid another miss?

This year, however, conscious that their ballots could again help decide the election, Michiganders of all political persuasions report being heavily motivated to vote. That’s a bad sign for Mr. Trump, who has never received a predominantly positive review from the roughly four in 10 Americans who identify as independents.

“Donald Trump didn’t win Michigan because there was a surge of Trump voters,” Richard Czuba, the founder of the Glengariff Group, a Lansing-based polling firm, said in an interview. “He won Michigan because there was a dearth of Democratic voters.”

Mr. Czuba gathers public opinion data each election year to calculate the average level of voter motivation, as reported by respondents using a 10-point scale. This month, a Glengariff poll for the television station WDIV and The Detroit News found that motivation levels in Michigan were nearly off the charts: Both Democrats and Republicans were averaging around 9.8, with independents not far behind at 9.2. In October 2016, the average for all voters hovered around 6.

Voters that year who leaned Democratic but weren’t strongly partisan averaged only 4.7 on the 10-point motivation scale, contributing to weak turnout for Mrs. Clinton in areas where she had expected to rack up votes.