Wisconsin insiders are expecting a slew of candidate announcements this week for the 2nd district seat of Rep. Tammy Baldwin (D), who announced her Senate candidacy today.

Three state legislators top the list of expected candidates: state Rep. Mark Pocan, state Sen. Jon Erpenbach and state Rep. Kelda Helen Roys.

The Madison-based district, which is heavily Democratic, hasn’t been an open seat since Baldwin first won it in 1998. Adding to the pent-up ambition of Dane County Democrats is the fact that the winner of the Democratic primary will likely have the seat for as long as they like.

Pocan replaced Baldwin in the state Assembly when she ran for Congress, and he said last week he’ll enter the race once she makes her Senate candidacy official. Like Baldwin, Pocan is gay and distinguished himself in the state Legislature for his leadership on progressive issues.

Erpenbach gained national notoriety during the collective bargaining rights debate with Gov. Scott Walker (R) earlier this year that led to 14 state Senate Democrats fleeing the state. He was interviewed on national TV shows, including the “Daily Show.” Like Pocan, Erpenbach was elected to the state Legislature in 1998.

Roys, a former executive director of NARAL Pro-Choice Wisconsin, was first elected to the Assembly in 2008. Other names will likely surface in the coming days, as heavily Democratic seats like this one don’t come open very often.

“The 2nd district race is wide open,” said Eric Hogensen, head of Milwaukee-based HSG Campaigns. “It seems like there’s a lot of great candidates who are elbowing their way into the mix. That’s really been the history of this district.”

Baldwin won a close four-way primary in 1998 for what was then a more competitive district. It improved for Democrats following the 2001 redistricting and was only solidified for the party in the current round of redistricting.