Republican Sen. Ron Johnson's campaign manager is expressing confidence to supporters while acknowledging the unpredictability of this election cycle.

Johnson campaign manager Betsy Ankeny also warns in the memo to supporters released Wednesday not to underestimate Johnson.

Johnson is considered vulnerable in his race against Democrat Russ Feingold, particularly because Johnson has never led in public polls by the Marquette University Law School. The memo was released just hours before the latest Marquette poll was to come out.

Ankeny said the campaign's internal polling has shown a tightening of the race since August, with Johnson now enjoying a slight lead. She also says the campaign is confident it has more money on hand than Feingold for the final weeks of the race.