Tomorrow, Wisconsin's primary is poised to do something it has not done in more than 30 years. It is about to deal a blow to a presidential front-runner.

Still more amazing is the fact the state's primary voters are expected to throw some shade on both the Democratic and Republican front-runners, an unimaginable result in the long era since World War II.

For six decades, Wisconsin has been anything but the field of dreams for long shots and outsiders. Wisconsinites have voted roughly halfway through the primary calendar, and they have almost always endorsed the candidates who were already winning.

Among Republicans, think Mitt Romney and John McCain, and both of the presidents named George Bush, plus Bob Dole, Ronald Reagan, Gerald Ford, Richard Nixon (three times) and Dwight Eisenhower.

Adding the Democrats, you have Barack Obama, John Kerry, Al Gore, Bill Clinton and Michael Dukakis — not to mention John F. Kennedy.

In fact, Wisconsin has been fine with the front-runner in both parties in every cycle since 1988. Setting aside one deviation on the Democratic side in 1984 (and the "favorite son" candidates who won on both sides in 1964) Wisconsin primary voters have fallen in line with the eventual nominees consistently since 1956 — long before most Americans alive today were even born.

Front-Runner Hopes May Be Dashed

This year, however, things suddenly look different. While Donald Trump and Hillary Clinton were ahead in the polls in Wisconsin as recently as early March, both have slid steadily downward since. Clinton has fallen behind rival Bernie Sanders by several percentage points, while Trump now trails Ted Cruz by double digits.

These trends are clear in the state's best-known and most reliable poll, done by Marquette University Law School. They are also corroborated in the latest polling by the Fox Business Channel and by CBS News. The polls could be wrong, of course, but they do also comport with field reports and other signals from the ground: Wisconsin is Cruzing and feeling the Bern.

Wins in Wisconsin should provide a major boost for both Cruz and Sanders, who can soar on the thermal updraft for two weeks before the next voting takes place.

Just how much momentum they gain in their still-steep climbs toward their party nominations will depend on the margins of their victories — and on the media treatment those results receive in New York, which votes on April 19. Both Trump and Clinton have maintained a kind of home-court advantage in New York despite their ups and downs around the country.

Given the trend in Wisconsin, wins for Cruz and Sanders will not have that element of surprise that supercharged them in Iowa (for Cruz) and Michigan (for Sanders). But winning big will contribute to the psychology now buoying both these long-shot candidates and their legions of true believers.

Winning margins in double digits tomorrow would constitute "winning big." So would a super-share of delegates for Cruz. Republican rules allow him 18 delegates for the statewide win and another three for each congressional district he carries. That makes it possible, if not likely, that Cruz could take home all 42 of the Wisconsin delegates.

There are several reasons for the Cruz and Sanders surge in this Midwestern purple state.

  • Trump has remarkably high negatives in the three "collar counties" outside Milwaukee that are the richest vein of Republican votes in the state. These suburban and ex-urban voters tend to be better educated, more affluent and much closer to the values of the GOP establishment than party voters outstate.
  • Trump has alienated much of the GOP base statewide by attacking the local hero, Republican Gov. Scott Walker. Trump went after Walker in the first several debates, and again this past week on the stump (after Walker endorsed Cruz). Walker's approval among state Republicans is in the range of 80 percent.
  • Wisconsin has a large and robust community of Christian evangelicals that has waited for a candidate like Cruz to embrace. It is now embracing Cruz.
  • For his part, Sanders can benefit from the strong preponderance of Anglo white voters among Wisconsin Democrats. No one doubts he will carry this dominant demographic on Tuesday.
  • Sanders benefits from the concentrations of younger voters in Dane County (the capital and home of the largest university campus), as well as satellite versions of same in other cities with University of Wisconsin campuses.
  • Sanders has devoted far more time and other resources to Wisconsin, eager to show that his recent dominance in five caucus states can be extended to a populous state where "open primary" rules allow independents to participate.

A Long History Of Confounding Candidates

Wisconsin also has a contrarian streak that has produced surprises in the past. While the primary has nearly always been won by the eventual nominee, Badger voters have also managed to send a message now and then that shook things up. In 2004, John Kerry solidified his grip on the Democratic nomination in Wisconsin's primary. But his 39 percent share of the multi-candidate vote barely edged John Edwards' 34 percent. Edwards said Kerry should realize that "objects in the rearview mirror are closer than they appear." Kerry subsequently chose Edwards as his running mate.

Forty years earlier, in 1964, one-third of the state's Democratic primary vote went to Alabama Gov. George Wallace, the segregationist who mounted a challenge to President Lyndon Johnson in protest of the civil rights bill then making its way through Congress. (Wallace ran again in the Wisconsin Democratic primary in 1972, receiving 22 percent of the vote to George McGovern's winning 29 percent).

Perhaps the two Wisconsin primaries that produced the most intense media attention in the past half-century took place in 1960 and 1976. The first contest matched neighboring Minnesota's Democratic Sen. Hubert Humphrey against the young upstart from Massachusetts John Kennedy. The latter won decisively, shifting the momentum of that year's nomination fight.

In 1976, liberal champion Morris Udall was a congressman from Arizona and a Mormon. He thought he had won the Wisconsin Democratic Party's nod when most people went to bed on primary night. But overnight that result was reversed, and in the morning Georgian Jimmy Carter was flashing his trademark smile under a copy of the Milwaukee Sentinel that erroneously reported Udall as the winner in a front-page banner headline.

Udall dropped out shortly thereafter, leaving Carter to march on to the nomination and the White House.

But Wisconsin has not always been such a bellwether. From 1912 until 1956, Wisconsin Republicans favored someone other than their party's eventual nominee. For several cycles, the state party preferred its own Robert "Fighting Bob" La Follette, a founder and favorite of progressive Republicanism.

Even after La Follette was gone, the state's GOP went for Midwesterners such as Harold Stassen or hard-line conservatives such as retired Gen. Douglas MacArthur (whose family had roots in the state) or Ohio Sen. Robert Taft. In 1952, the Wisconsin GOP preferred Taft to Dwight D. Eisenhower. After Ike won the nomination and the presidency that year, he was able to win the Wisconsin primary in 1956 — the first eventual nominee of his party to do so.

The Badger State's reputation is steeped in politics at the edge: The visionary progressive La Follette was a demigod on the left, while the amazingly charismatic anti-communist Joseph R. McCarthy was and is an icon on the right.

But in practical terms, most of Wisconsin's governors and senators have tended to be closer to the mainstream of their respective parties. While the state is known for ideological partisanship, two Democrats, William Proxmire and Herbert Kohl, held one of its two U.S. Senate seats for more than half a century (1957-2012) while functioning as self-defined independents.

It is this independent element of Wisconsin's complex political identity that has informed the results of its quadrennial presidential primary. As the state does not register voters by party, it has always been part of the local tradition to hold an "open primary" for president.

Voters can sign in on primary day, take a blank ballot for each party, fill one out and discard the other. The clerk in the precinct never knows which ballot each voter has actually used.

Given this tradition, and the state's mid-position on the calendar, Wisconsin has nearly always served as the confirmation of the front-runner's inevitability.

The only cycle after 1952 when Wisconsin did not presage the GOP nominee was 1964, when the state party chairman got a popular congressman to run as a "favorite son" and then persuaded both of the party's leading national candidates (Barry Goldwater and Nelson Rockefeller) to stay out of the state for the sake of unity. Both did.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.