SCOTT SIMON, HOST:

On to Wisconsin. Presidential candidates from both parties are campaigning there this weekend. Republicans especially view it as a contest that could play a huge, huge role in determining whether Donald Trump wins the delegates he needs to secure the nomination before this summer's convention. Ted Cruz and John Kasich both attended a real Wisconsin event last night, the fish fry at Milwaukee's famous Serb Hall. NPR's Scott Detrow was there and joins us from Milwaukee. Milwaukee, I should say. Good morning, Scott.

SCOTT DETROW, BYLINE: Morning, Scott.

SIMON: And I hope - I've been to that fish fry a couple times - I hope you knew enough, my friend, not to order the line-caught Mediterranean steamed sea bream.

DETROW: (Laughter) I stayed away from that. I always prefer the lake perch at a fish fry, but they had some good haddock there. You know, this was billed as the largest fish fry in the state. And Serb Hall is really an iconic campaign stop in Wisconsin. In fact, they've got portraits on the walls of every single president who's campaigned there. And there's a chapter in Hunter S. Thompson's famous campaign trail book, "Fear And Loathing On The Campaign Trail," that takes place at a George Wallace rally at Serb Hall.

SIMON: We keep hearing Wisconsin is pivotal, and Mr. Trump said so himself earlier this week.

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DONALD TRUMP: Wisconsin is very important. It's becoming more and more important.

SIMON: So how important? Because, you know, much bigger states, including New York and California, are ahead in the primary calendar.

DETROW: That's right. It's about its place on the calendar and kind of the way that the race has kind of narrowed down to basically a two-person contest between Donald Trump and Ted Cruz. Trump has a path to clinch the nomination before the convention, but it's very narrow. There's not much room for error. You mention, you know, New York coming up ahead. There's a series of states where Trump expects to do well.

But here in Wisconsin, Ted Cruz has really gotten a lot of momentum. He's basically doubled in the polls over the last month. And there's a lot of delegates at stake - 42 delegates - and Ted Cruz has a chance - it's narrow but there's a chance that he could pick up all 42 if he does well statewide and in all the congressional districts. And if Cruz gets those delegates, that really puts a dent in Donald Trump's path to the 1,237 delegates he needs to prevent a contested convention and a big floor fight.

SIMON: And what kind of reception did Senator Cruz get in Milwaukee last night?

DETROW: He was a big hit. This was the Milwaukee Republican Party. And it was clear that most of them, Ted Cruz is their guy. You know, they gave John Kasich polite applause. Sarah Palin was there as a surrogate for Donald Trump. And there was basically near silence for her. It was actually kind of awkward in the room.

But when Scott Walker, the governor of Wisconsin, introduced Cruz, the crowd was on its feet, they were cheering the whole time. And Walker made a point to say that he's not just anti-Trump, he's pro-Cruz. But Ted Cruz is definitely benefiting from growing concern from some pockets of Republicans about Donald Trump as a nominee, how he would do for the party in November. And that's something that Cruz directly spoke to last night in Milwaukee.

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TED CRUZ: For the 65 to 70 percent of Republicans nationwide who recognize that nominating Donald Trump is a train wreck, that's actually not fair to train wrecks...

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CRUZ: ...That nominating Donald Trump elects Hillary Clinton, Hillary not only wins, she wins by a big margin.

SIMON: John Kasich is a Midwestern governor. Wisconsin ought to be in his wheelhouse.

DETROW: That's right. And if you look at what John Kasich has done as governor of Ohio, it's actually pretty similar to what Scott Walker has gotten passed in Wisconsin that's made him so popular with the party there.

But the thing is, the Trump opponents really seem to be coalescing around Cruz and that's due to the fact that Kasich is just so far behind in the delegate count. He's only won his home state. Kasich argues it doesn't matter. As long as he gets to the convention and there's no nominee, he should be in play.

SIMON: And just a few seconds left, let's not forget the Democratic race because Bernie Sanders is coming off a string of victories and has a ton of money.

DETROW: That's right. And the polls show a really close race here with Bernie Sanders actually ahead. He's hoping to continue a streak of several wins. The thing is he needs to win by very wide margins in every state going forward in order to catch Hillary Clinton.

SIMON: NPR's Scott Detrow in Milwaukee. Thanks so much.

DETROW: Thank you, Scott. Transcript provided by NPR, Copyright NPR.