Feingold still leads the poll by a single-point margin, 45-44, with Libertarian Phil Anderson trailing at 3 percent.
The Republican senator showed signs that he was approaching Feingold's lead in Marquette's early October poll, where Feingold led by two points in both the head-to-head and third-party matches. But at the same time, a Monmouth University poll from mid-October showed the former Democratic senator ahead by eight points.
The Marquette University poll was conducted Oct. 26-31 among 1,255 likely Wisconsin voters via live telephone interview, with a margin of error of plus or minus 3.5 percent.
TPM's PollTracker Average for the U.S. Senate election in Wisconsin shows Feingold leading Johnson, 47.7 to 43.6.