Politico's Jim VandeHei calls Wisconsin "the race that says it all." More than any other Senate race, he writes, what voters are saying in Wisconsin distills the last two years of American political life down to their purest essence.
Ron Johnson, a conservative, politically inactive businessman gets mad about the government's response to the economic collapse, finds himself caught up in the Tea Party movement, writes an essay on health care, and suddenly finds himself the toast of statewide talk radio. Within months, he's the Republican nominee for senator, and within weeks, he's beating the incumbent by a healthy margin. He's a hard-right candidate who utters all the apocalyptic tropes: Washington Democrats are "socialists." The health care bill will "destroy" the system. Johnson is a staunch social conservative, too.
Meanwhile, Russ Feingold is doing everything Democrats say Democrats should be doing: running on their record of accomplishment, running WITH President Obama, not away from him, bragging about health care. Democrats are targeting young voters and surge voters with vigor and money.
Atmospherically, the bottom has fallen out for President Obama among white voters in the state -- a state he won in the general election as well as in the primary, thanks to the young voter surge. The generational split is in evidence here: young voters are depressed about their job prospects and older voters resent spending programs that will pay for young voters' future opportunities. As VandeHei notes, conservatives have managed to brand themselves as the ideological carriers of anger at government and spending, so independents have migrated to the right. Attempts by Democrats to scare people about Johnson -- he's crazy, too right wing, etc. -- don't work in this environment.
In general, the gains Democrats have made over the past four years with whites who don't have college degrees have disappeared, thanks to the drag of the Democratic brand. If Wisconsin reverts back to type, it will be nearly impossible for Democrats to win in 2012. More generally, Wisconsin is the type of race that will determine how the 2010 elections are interpreted. It is generally free of some of the extraneous factors that make races like Colorado (Michael Bennet has never won an election before) or Nevada (Harry Reid's programs aren't cycle-specific) excusable.
If Feingold loses, it will be because Wisconsin Republicans, and enough independents, turned out to veto President Obama and the Democratic Party, period, end of sentence. That's not the template the White House will want to start with after November.