MADISON, Wis. — The April 5 Wisconsin Presidential primary is emerging as a crucial lifeline for Republicans desperate to stop Donald Trump’s march to their party’s nomination. One of his worst weeks of the 2016 campaign is colliding with a state already skeptical of his brash brand of politics.

A big loss for Trump in Wisconsin would greatly reduce his chances of securing the delegates he needs to clinch the GOP nomination before next July’s national convention. It could also offer new hope to rival Ted Cruz and outside groups that see Trump as a threat to the future of the Republican Party.

“I think the whole country is looking to Wisconsin right now to make a choice in this race, and I think the choice Wisconsin makes is going to have repercussions for a long time to come,” Cruz said in an interview with Milwaukee radio station WTMJ.

Trump’s view is rosier for his own campaign: “If we win Wisconsin, it’s pretty much over.”

But almost nothing has gone right for him since Wisconsin stepped into the primary spotlight.

Even before he arrived, Trump was skewered in interviews with a trio of Wisconsin’s influential conservative talk radio hosts. On March 29, just hours before his first campaign stop, two-term Gov. Scott Walker threw his support behind Cruz, of Texas.

Much of the trouble that followed was of the Trump campaign’s own making. Corey Lewandowski, Trump’s campaign manager, got slapped with a charge of simple battery for an altercation with a reporter.

Then Trump was forced to walk back his assertion that women should be punished for getting abortions, a comment that managed to unite both sides of the abortion debate in fierce opposition to his statement.

“As soon as he stepped foot in Wisconsin the mask finally came off,” said state Rep. Jim Steineke, the Republican majority leader in the Wisconsin Assembly. “Part of it is just the Wisconsin nice. We don’t take too kindly to people who act the way Donald Trump acts.”

GOP voter Linda Ruddy, a 48-year-old dental hygienist from Oshkosh, agreed. “He’s rude. He’s arrogant. He’s a loose cannon. He’s insulting to women,” Ruddy said.

A poll run by Marquette University Law School has shown Trump holding steady at around 30 percent in Wisconsin, a level of support that gave him a lead in the state last month. But the latest survey released this week showed Cruz surging past the real estate mogul, topping him by 10 points.

“Everybody is going to want to write that he got taken down,” Cruz Campaign Manager Jeff Roe said of Trump. “The fact is he didn’t get taken down. The fact is that we’re consolidating.”

If Cruz sweeps all the delegates in Wisconsin, Trump will need to win 57 percent of the remaining delegates in other states to collect the 1,237 he needs to clinch the nomination. So far, he has won 48 percent of all delegates awarded.

Wisconsin offers 42, putting it in the middle of the pack of primary prizes. But the state’s stature in Republican politics and its position on the calendar — no other state votes until April 19 — have elevated its importance.

Though the state has voted for Democrats in the past several presidential elections, it boasts prominent national party leaders including Walker, House Speaker Paul Ryan and Republican National Committee Chairman Reince Priebus.

Anti-Trump groups say they have benefited from the primary calendar. Super PACs and rival campaigns have been able to focus narrowly on Wisconsin for nearly two weeks.

Planned Parenthood and Priorities USA, two groups working to elect Hillary Clinton, have teamed up for their first anti-Trump advertisement of the election year, a 30-second spot playing on websites that features Trump’s abortion comment.

“When it comes to women, the Republican front-runner is demeaning, insulting and dangerous,” the ad reads.

Clinton herself is hardly silent. She said March 31 in Purchase, New York: “Donald Trump is showing us exactly who he is and we should believe him. But let’s remember this, all the Republican candidates want to make abortion illegal.”

Trump’s rival candidates and outside groups opposing him are slated to spend a combined $3.8 million in advertising in the state.

That includes about $1.7 million from Our Principles and Club for Growth Action, a conservative group that has endorsed Cruz.

So far, the billionaire’s campaign is slated to spend only about $430,000 on radio and television advertising leading up to the primary, according to data from Kantar Media’s Campaign Media Analysis Group.

Trump’s largest presence on TV has been an ad that touts his proposed temporary ban on Muslims entering the U.S.

But Trump will soon get some help. A super PAC supporting him said it would start running two different television ads over the weekend as part of a seven-figure nationwide buy.

After Wisconsin, the real estate mogul will find himself back in friendly territory, with the April 19 primary in New York

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By Scott Bauer and Julie Pace. AP writers Thomas Beaumont, Ken Thomas, Chad Day, Stephen Ohlemacher and Julie Bykowicz contributed