Former Wisconsin Sen. Russ Feingold will not run for any state or federal office in 2012, at a time with an open Senate seat and a potential gubernatorial recall election.

In an email going out to supporters early Friday morning, Feingold called it a difficult decision but said he wanted to devote his time to teaching full time at Marquette Law School, finishing the book he is writing on the U.S. response to the Sept. 11 attacks and leading the political committee he founded, Progressives United.

“While I may seek elective office again someday, I have decided not to run for public office during 2012,” Feingold said in the email.

Some Democrats were looking to Feingold as perhaps their leading candidate against Walker next year in the event of a successful recall drive. His announcement ends that scenario.

Feingold has built an organization in Progressives United that is dedicated to fighting corporate money in politics. He clearly feels he can do his best work from the outside. It’s definitely a fight that needs to be waged.

As we have seen, Feingold was the candidate who performed best in polls in both the Senate and Governor races in Wisconsin. There are other options there, but they start out behind.

For the gubernatorial recall, the next likely candidate in line is Milwaukee mayor Tom Barrett, who lost the 2010 election to Scott Walker. It remains to be seen when a recall would take place or even if, as the outrage at Walker and his actions has faded somewhat.

As for the Senate, Herb Kohl is retiring. The likely Democratic candidates are Reps. Tammy Baldwin, who would become the first openly gay Senator in history, and Ron Kind. Baldwin probably has the edge in a primary because of her base in Madison. The likely Republican candidate is former Governor, Secretary of Health and Human Services and corporate lobbyist Tommy Thompson, who has been putting together a team for a run.

Thompson will have to get past a primary, where tea party conservatives might choose a more loyal candidate (other potential options include former state Senator Ted Kanavas, former Congressman Mark Neumann and even one of the Fitzgerald boys, who run each house of the legislature). But if he does, Thompson does best in a general election, leading all comers by 7-8 points, according to Public Policy Polling.

Some of that is due to name recognition, and to be honest, that was part of Feingold’s better numbers too (he was tied with Thompson in that round of polling). But it does show that the Wisconsin Senate seat will be another difficult hold for Democrats, in an election year with tough races all over the country. In fact, Democrats might want that Scott Walker recall on the ballot just to boost turnout for the Senate race.