MADISON, Wis. — Republican Governor Scott Walker of Wisconsin has been warning for months about a ‘‘blue wave’’ coming this fall, but so many Democrats are eager to ride it that it is a struggle for any dominant challenger to emerge.

Eight Democrats are taking on Walker as he seeks a third term, a sign of just how badly the party wants to dethrone one of the GOP’s most recognizable governors. Walker’s strong anti-union moves made him a demon to the left and catapulted him to the national stage for a brief 2016 presidential run.

State schools chief Tony Evers, who has skirmished with Walker on a number of issues over the years, enters Tuesday’s primary as the best-known Democrat. Though he leads in polls, many voters are undecided, and some challengers are counting on a surge from younger voters to help them topple the 66-year-old Evers.

‘‘We’ve been ignored by out-of-touch politicians,’’ said Kelda Roys, a 39-year-old former state lawmaker who got noticed early in the campaign with a video that showed her breastfeeding her daughter. Roys argues she is the one to appeal to millennials, Gen Xers, and suburban married women.

The primary will serve as a test of Democratic enthusiasm in a state that has long been associated with liberal politics but has been trending red and narrowly voted for President Trump in 2016. The large field of Democratic challengers to Walker is the latest example of the energy in the party.

Associated Press