Clinton leads Trump by 15 percentage points, 52% to 37%, among likely voters -- with 10% supporting neither candidate. That's a huge jump from the same poll's findings in July, when it had Clinton at 45% to Trump's 41%.
Among registered voters, Clinton leads by 10 points, 46% to 36%.
Wisconsin, which has historically supported Democratic presidential candidates, is a state where Republicans have had some recent success -- with Gov. Scott Walker winning two statewide gubernatorial races, as well as his own recall election.
But it's been tough for Trump, who lost Wisconsin's April presidential primary to Texas Sen. Ted Cruz amid intense opposition from the state's influential and united set of anti-Trump conservative talk radio hosts.
Trump is viewed favorably by just 27% of Wisconsin's registered voters, while 65% view him unfavorably.
Clinton's favorability rating is underwater, too -- but it's better than Trump's, at 43% favorable, 53% unfavorable.
The poll underscores Clinton's continuing weakness: trustworthiness. Only 32% said "honest" describes her; 64% said it does not.
But Trump has the exact same problem: 33% said "honest" describes him; 64% said it does not.
The survey also found a big gap in voters' views of whether Clinton and Trump are qualified for the presidency. Of registered voters, 58% said Clinton has the qualifications to be president, while just 29% said that of Trump.
The poll found Wisconsin as a prime pickup opportunity for Senate Democrats, too. Democratic challenger Russ Feingold leads Republican Sen. Ron Johnson, 53% to 42%, among likely voters. With registered voters, the race is at 49% Feingold, 43% Johnson.
The poll was conducted August 4-7. It included 801 registered voters, with a margin of error of plus or minus 4.7 percentage points. Of those, 683 said they were certain to vote. Those were classified as likely voters, with a margin of error of plus or minus 5 percentage points.