Had Wisconsin Senator Herb Kohl’s current term concluded at a politically calmer moment in the state’s history and had the 76-year-old senior senator made his surprise decision to step down in that moment, the race to replace the popular Democrat would have followed the predictable patterns for which a generation of Wisconsin politicians has been preparing.


Congressman Paul Ryan, R-Janesville, would have been his party’s choice to replace Kohl.


Congresswoman Tammy Baldwin of Madison, running from the progressive wing of the Democratic Party, and Congressman Ron Kind of La Crosse, running from the more Wall Street-friendly wing, would have competed with one another for their party’s nomination. Baldwin probably would have won, thanks to a decision to back her by unions that have long been frustrated with Kind’s support for corporate-sponsored free-trade deals.


The ensuing November contest would have been an epic partisan and ideological struggle, featuring all the big-money, outside spending and political positioning that characterizes the nation’s most important Senate races.


But this is not a politically calm moment in Wisconsin history.


That does not mean that the race to replace Kohl, who announced Friday that he will step down next year at the end of his fourth term, won’t be an epic partisan and ideological struggle. Nor does it mean that anyone should count Ryan, Baldwin or Kind out of the competition.


It does, however, mean that there will be more to this competition than might otherwise have been expected.


Here’s why:


1. Former Senator Russ Feingold, an iconic figure among left-leaning Wisconsinites and a traditionally popular contender among independent voters, was swept out of office in the 2010 Republican wave. That was a tough loss for Feingold, who was not ready to leave the Senate, and a tougher one for his backers, who see him as the embodiment of the state’s progressive tradition.


From the moment his defeat was confirmed last November, Feingold backers in Wisconsin -– and far beyond the state’s borders -– were looking for a way to return the opponent of corporate excess, the Patriot Act and the Afghanistan and Iraq wars to office. Almost every conversation about Feingold began with the phrase: “If Herb Kohl doesn’t run…” Now, he’s not running and Feingold must make a definitional decision, not just about his own political future but about Wisconsin’s political future.


2. Ryan was for more than a decade the "golden boy" of Wisconsin politics. Yes, he was a conservative ideologue. But he was, as well, a charming young man with exemplary political skills and, because of his willingness to carry Wall Street’s agenda as a key player on the House Budget Committee, had ready access to all the campaign money he was going to need to mount a serious Senate run.


Then, Ryan came up with a politically toxic proposal to radically restructure the nation’s popular Medicare program. Polls found that 80 percent of Americans opposed Ryan’s scheme, and the angry crowds the congressman encountered at April town meetings across southeast Wisconsin suggested that his “golden boy” image was tarnished.


3. Gov. Scott Walker, elected in November by a comfortable margin, proposed in February to strip state, county and municipal employees and teachers of workplace rights, and then he proposed in March to pay for corporate tax breaks by imposing deep cuts to local schools and public services. The governor’s initiatives sparked the largest and most sustained mass protests in the modern history of the United States, crashed the executive’s approval ratings and led thousands of Wisconsinites to slap “Recall Walker” stickers on the bumpers of their cars.


While it is not uncommon for governors to be considered as contenders for open Senate seats — even governors who are at the start of their terms –- Republicans in Washington and Wisconsin have shied away from even mentioning him in initial speculation about who their party would nominate to fill the Kohl seat.


And Republican officials associated with Walker, including Lt. Gov. Rebecca Kleefisch, face the prospect of having to distance themselves from the governor and the controversies surrounding him.


So where does that leave Wisconsin politicians as they prepare for what is likely to be one of the most serious Senate contests of 2012?


In a very volatile place.


And that volatility may last for a long time.


For Democrats, the question of whether Feingold is going to run will need to be settled one way or another before their race begins. The former senator is getting pressure already; he had a call Friday from Senate Majority Leader Harry Reid, D-Nevada, with whom he was reasonably close when they both served in the Capitol. Reid and other Washington Democrats would love to have Feingold run. He’s a known entity with a national fund-raising base –- enhanced by his new activist group, Progressives United –- and there is a general sense that the only reason he lost in 2010 was because of the Republican wave that swept through so many Great Lakes and Midwestern states last year.


Feingold is certainly viable. And there are already “Draft Russ Feingold” campaigns ginning up on the Internet. The group Democracy for America was out front, emailing members Friday with a message that read: “Earlier today, Democratic Sen. Herb Kohl announced he was retiring after 24 years in Washington. Thankfully, there’s a progressive champion waiting in the wings to step up and keep this seat for the Democrats in 2012: Russ Feingold.”


Citing Feingold’s “progressive legacy” as “the only Senator to vote against the Patriot Act, a national leader for campaign finance reform and against the war in Iraq, and so much more,” the group (which grew out of Howard Dean’s 2004 presidential run and has a number of chapters in Wisconsin) is urging members to sign a petition encouraging the former senator to jump in the race.


But Feingold is not a certain contender.


After almost three decades in elected office, he is enjoying teaching at Milwaukee’s Marquette Law School, writing a book on foreign policy and frequent travel to destinations he rarely visited as a senator.


The notion that Feingold is hungry to make this run is not accurate. He might do so, but there are no guarantees.


That means that other Democrats who have long had an interest in the seat, especially Baldwin and Kind, are very real prospects. It is no secret that Baldwin is interested in succeeding Kohl. And she’s a credible contender. A favorite with liberals, she has a base in vote-rich Dane County. She would, as well, get boosts from groups such as Emily’s List and national lesbian and gay groups that would be excited to elect that first openly gay or lesbian senator.


But Kind is one of the state’s most determined campaigners and he has a base of his own among business-friendly Democratic groups that share longtime Democratic Leadership Council ally’s willingness to break with organized labor on trade issues.


Additionally, some of the “Fab 14” state senators who opposed Walker’s agenda have become political superstars. That’s certainly true of state Sen. Jon Erpenbach, a Dane County Democrat who was broadly seen as having acquitted himself well in the media spotlight. Milwaukee Sen. Chris Larson also has a lot of fans, although he is not yet old enough to meet the constitutional requirement that senators be 30 years of age. (He will be old enough by next year, however.)


Other longtime Democratic political players will also be in the mix. Former Governor Jim Doyle will get some mentions, although he has little base of active support among party activists. Milwaukee Mayor Tom Barrett, who lost last year to Walker, is more popular with the base. And former Lieutenant Governor Barbara Lawton is a genuine favorite. Lawton could be a contender. So, too, could former Superintendent of Public Instruction Elizabeth Burmaster, who has run and won statewide as a nonpartisan candidate but is popular with Democrats and unions.


And don’t rule out former Dane County Executive Kathleen Falk, who narrowly lost a 2006 race as the Democratic nominee for attorney general and ran well for governor in the 2002 race for the Democratic gubernatorial nod.


On the Republican side, Ryan might yet be a runner. He teased a bit on Friday, issuing a statement that left the prospect open: “I was surprised by Senator Kohl’s announcement and want to take some time over the next few days to discuss this news with my family and supporters before making any decision about how I’m best able to serve my employers in the First Congressional District, our state and nation."


Ryan is a Capitol Hill veteran and he knows this may be his only chance in a long time to jump to the Senate. But entering the race to replace Kohl would draw the House Budget Committee chair’s attention away from the fiscal fight in which he is currently so central. And that weighs against making the race this time.


If Ryan decides not to seek the Republican nod -– a prospect that might not bother GOP strategists considering the controversy surrounding his Medicare and Social Security stances — the man who beat Falk in 2006, Attorney General J.B. Van Hollen, could be the most serious Republican runner. He has won twice statewide, and in 2010 was the party’s strongest vote-getter. He is, as well, a native of northern Wisconsin with a base in a region that often votes Democratic. Van Hollen seems to be considering the race; an aide said Friday: "The attorney general is keeping his options open. There’s been a great deal of encouragement for him to run so he’s weighing the opportunity."


The Republican congressional delegation includes two freshmen who might be considered possible candidates: Sean Duffy and Reid Ribble. But Duffy has stumbled in recent public appearances -– complaining about his congressional pay, among other things -– and Ribble does not seem to have the Senate bug.


The senior member of the GOP delegation, conservative Jim Sensenbrenner, has skipped Senate races in the past, and U.S. Rep. Tom Petri, R-Fond du Lac, is too moderate to win a party primary.


Several Republican legislators, including Senate Majority Leader Scott Fitzgerald, R-Juneau, are considering runs. Fitzgerald’s brother, Jeff, who is the Assembly Speaker, says through an aide that he would “definitely consider” entering the race if Ryan does not. But the wrangling over collective bargaining and the state budget makes both Fitzgeralds controversial contenders.


Former state Sen. Ted Kanavas, one of the GOP’s ablest political players, has signaled that he is interested.

Former U.S. Rep. Mark Neumann, who lost to Walker in last year’s Republican gubernatorial primary, seems to be “in.” “It is no secret that I have been seriously considering entering the race for U.S. Senate," Neumann said in a statement. "It is a decision I will not take lightly. The future of our state and our nation is at stake."


But Neumann has already lost a Senate race -– to Feingold in 1998. And the party is unlikely to settle for him this time. Grabbing the Wisconsin seat is too important to the GOP’s national goal of taking control of the Senate from the Democrats.


That brings us to Tommy Thompson. The former governor and Bush administration cabinet secretary remains popular statewide and has better name recognition than anyone save Feingold. He considered running in 2010 but decided to skip the race. Could he be drawn in by the promise of a likely win, especially if Feingold decides against a 2012 race? This is an open question. But rest assured that, as he has so frequently over the years, Thompson will keep everyone guessing for awhile.


In the case of this Senate contest, however, Thompson won’t be the only one keeping the speculation going. In what is already one of the most intense political seasons in Wisconsin history, the mildest of political players, Herb Kohl, has just guaranteed that things won’t calm down until November 2012.