(AP) -- Republican Ted Cruz stormed to a commanding victory in Wisconsin Tuesday, denting front-runner Donald Trump's chances of capturing the GOP nomination before the party's convention. Bernie Sanders carried the Democratic race over Hillary Clinton, a win that still leaves him with a mathematically difficult path to the White House.

Trump's defeat capped one of the worst periods of his campaign, a brutal stretch that highlighted his weaknesses with women and raised questions about his policy depth. While the billionaire businessman still leads the Republican field, Cruz and an array of anti-Trump forces hope Wisconsin signals the start of his decline.

"Tonight is a turning point," Cruz told cheering supporters at a victory rally. "It is a call from the hardworking people of Wisconsin to America. We have a choice. A real choice."

For Sanders, Wisconsin was the latest in a string of victories that have given him an incentive to keep competing against Clinton. But he still trails her in the pledged delegate count and has so far been unable to persuade superdelegates-- the party officials who can back any candidate -- to drop their allegiance to the former secretary of state and back his campaign.

The results in Wisconsin make it likely both parties' primaries will continue deep into the spring, draping front-runners Trump and Clinton in uncertainty and preventing both from fully setting their sights on the general election.

For Sanders, Wisconsin was favorable territory, with an overwhelming white electorate and liberal pockets of voters, and the Vermont senator's victory gives him a fresh burst of momentum.

Because Democrats award delegates proportionally, Sanders and Clinton will both emerge from Tuesday's contest with more delegates.

Heading into Wisconsin, Clinton had 1,243 to Sanders' 980 based on primaries and caucuses. When including superdelegates, the party officials who can back any candidate, Clinton holds a much wider lead -- 1,712 to Sanders' 1,011. It takes 2,383 delegates to win the Democratic nomination.

Clinton's campaign has cast her lead as nearly insurmountable. Yet Sanders' continued presence in the race has become an irritant for the former secretary of state, keeping her from turning her attention to the general election.

According to exit polls, Sanders has excited voters in Wisconsin, with more than half of Democratic primary-goers saying the senator inspires them more about the future of the country. But three-quarters of Democratic voters say Clinton has realistic policies.

The exit polls were conducted by Edison Research for The Associated Press and television networks.

Trump has battled a series of campaign controversies in the lead-up to Wisconsin, including his campaign manager's legal problems following an altercation with a female reporter and his own awkward stumbles in clarifying his views on abortion. Wisconsin's Republican establishment, including Gov. Scott Walker, has also campaigned aggressively against the businessman.

Exit polls in the state underscored the concerns about Trump that are surging through some corners of the Republican Party. Nearly 4 in 10 GOP voters in Wisconsin said they were scared about what Trump would do as president.

Complicating the primary landscape for both Cruz and Trump is the continuing candidacy of John Kasich. The Ohio governor's only victory has come in his home state, but he's still picking up delegates that would otherwise help Trump inch closer to the nomination or help Cruz catch up.

If Cruz wins all of Wisconsin's 42 delegates, Trump would need to win 57 percent of those remaining to clinch the GOP nomination before the July convention. So far, Trump has won 48 percent of the delegates awarded.

To win a prolonged convention fight, a candidate would need support from the individuals selected as delegates. The process of selecting those delegates is tedious, and will test the mettle of Trump's slim campaign operation.

Cruz prevailed in an early organizational test in North Dakota, scooping up endorsements from delegates who were selected at the party's state convention over the weekend. While all 28 of the state's delegates go to the national convention as free agents, 10 said in interviews that they were committed to Cruz. None has so far endorsed Trump.

Despite the concern among some Wisconsin Republicans about Trump becoming president, nearly 6 in 10 GOP voters there said the party should nominate the candidate with the most support in the primaries, which so far would be Trump. Even among voters who favored Cruz, 4 in 10 said the candidate with the most support going into the convention should be the party's nominee.

___

Pace reported from Washington. Associated Press writers Jill Colvin, Jonathan Lemire, Hope Yen, Stephen Ohlemacher, Bryna Godar and Greg Moore contributed to this report.

___

Follow Julie Pace and Scott Bauer on Twitter at: http://twitter.com/jpaceDC and http://twitter.com/sbauerAP