Hillary Clinton has lost more than half of the 13-point lead she carried over Donald Trump in Wisconsin in the middle of August, according to a new Marquette University Law School poll.

The former secretary of state now leads Trump 45-42 percent among likely voters in the Midwestern battleground, after edging him 47-34 percent in a previous poll released on Aug. 10. Nearly 20 percent of registered voters in the Badger State in the latest poll said they will not vote for Clinton or Trump in the November election.

A separate Monmouth University poll released Wednesday also showed Clinton's lead narrowing in Wisconsin. The Democratic presidential hopeful led Trump by 5 percentage points — 43-38 percent — among likely voters in that poll.

Meanwhile, the Marquette Law School poll shows the U.S. Senate race between incumbent Republican Sen. Ron Johnson and Democrat Russ Feingold tightening. Feingold led Johnson by 9 percentage points among likely voters in mid-August, but he now carries a slim 3-point lead of 45-42 percent.

The poll of 803 registered Wisconsin voters was conducted Aug. 25-28. Results contain a margin of error plus or minus 4.5 percentage points.