AMNA NAWAZ: Finally, Lisa, we know that you have just returned from a key state in this midterm election year, Michigan.

What should we know?

LISA DESJARDINS: This was fascinating.

We found Democrats in Michigan wrestling over an absolutely critical and intense Senate race.

Their primary is tomorrow between two candidates who both say they're underestimated, but it's really about how Democrats try to win and who they want to be.

LISA DESJARDINS: In Michigan, is this a phase or is this the future?

ABDUL EL-SAYED (D), Michigan Senatorial Candidate: All right, so money out of?

AUDIENCE: Politics!

ABDUL EL-SAYED: Money in your?

AUDIENCE: Pocket!

ABDUL EL-SAYED: Medicare for?

AUDIENCE: All!

ABDUL EL-SAYED: That's what we're fighting for.

You all, it just shouldn't be this hard.

LISA DESJARDINS: Abdul El-Sayed is many things, a Michigan native, a Rhodes Scholar with a medical degree, and a former public health director.

Vigor is his brand.

A progressive who's never held office before, he is banking on enthusiasm.

DORICE STEINER, Abdul El-Sayed Supporter: He's authentic.

He doesn't owe anything.

He's not representing anyone but the people.

BRUNO NAVARRE, Abdul El-Sayed Supporter: He's not just like, hey, I'm pushing the same buttons as everyone else.

He's actually like, hey, this is messed up.

You have got to fix this.

LISA DESJARDINS: Battling him is Congresswoman Haley Stevens.

REP.

HALEY STEVENS (D-MI), Senatorial Candidate: We all know we're a swing state, and we're going to win big in November.

LISA DESJARDINS: Her brand is hard worker, can-do, as in 2018, when she flipped a Republican district to win her U.S.

House seat, or, in 2009, when she helped run President Obama's auto bailout.

Stevens leans in on her record and her Michigan accent.

REP.

HALEY STEVENS: I have this community's back.

I have this state's back, and I'm going to lead in the way we need and deserve.

I'm going to stick it to them.

LISA DESJARDINS: Her supporters say she's the one who can win in the fall.

SUSAN ANDERSON, Haley Stevens Supporter: There's no contest.

She has a proven record.

TYLER MCCASTLE, Haley Stevens Supporter: Fighter for the working man or woman.

She really stands up for that.

LISA DESJARDINS: One party choosing from two different directions.

CINDY GROENE, Haley Stevens Supporter: I have got friends on both sides.

LISA DESJARDINS: And they feel strongly.

CINDY GROENE: And they feel very strongly about their choice.

LISA DESJARDINS: In the Detroit suburbs, Cindy Groene is highly engaged.

She volunteers and campaigns with the local Democratic Party, and she's supporting Stevens.

CINDY GROENE: I feel strongly that she's the right choice.

One is her policies.

And the other is I feel she has the best chance of winning the race once the primary is over.

LISA DESJARDINS: How important is that?

CINDY GROENE: I think it's critical.

The state is a purple state, and I think it's going to be close.

LISA DESJARDINS: Polling backs that up.

A recent Michigan Education poll found Stevens neck-and-neck with Republican Mike Rogers.

He's a former congressman who narrowly lost a Senate race two years ago and has President Trump's endorsement.

In the same poll, Abdul El-Sayed trailed Rogers by 10 points.

ABDUL EL-SAYED: It is hard past time for us to show up and start taxing billionaires their wealth.

LISA DESJARDINS: But El-Sayed says this misses his momentum.

ABDUL EL-SAYED: The way you win is to bring more voters to the coalition and to win some of these folks who want a politician who's not bought off.

I will also tell you this that to beat somebody like Mike Rogers, you actually have to offer a contrast.

If you need $60 million, as my Democratic opponent has taken, to barely be competitive in a primary, tell me how you're electable again.

LISA DESJARDINS: This is one of the most expensive Senate primaries in history, fueled not just by divide over the Democratic Party's direction, but by one high-stakes debate over Israel and Gaza.

NARRATOR: She's fighting back against Trump's Medicare cuts.

LISA DESJARDINS: This ad may not mention the Middle East, but the super PAC involved is focused on it.

Tied to AIPAC, or the American Israel Public Affairs Committee, the group has spent more than $30 million for Stevens and against El-Sayed.

NARRATOR: That's the real Abdul El-Sayed.

LISA DESJARDINS: The outside spending is sparking wide backlash.

At the same time, Democrats are divided over Gaza.

El-Sayed sharply criticizes America's role in providing weapons to Israel.

ABDUL EL-SAYED: Antisemitism is a scourge and we must stand up against it.

But this is about love for the people who go without those basic things in America.

So how dare we ask how we're going to pay for improvements to our schools or health care while we don't bat an eyelash to sending $3.3 billion of our taxpayer money to a foreign government doing genocide and apartheid.

LISA DESJARDINS: Aleena Malik's a rising senior at the University of Michigan studying business.

While home for the summer, El-Sayed inspired her to canvass for the first time.

ALEENA MALIK, Abdul El-Sayed Supporter: I was definitely scared going into it, but it was really nice.

LISA DESJARDINS: A core issue for her, the AIPAC and corporate money in this race.

ALEENA MALIK: I didn't realize how campaigns were funded and how they can be funded by these corporate political action committees and how that can affect the policies that are made.

REP.

HALEY STEVENS: I'd love a constitutional amendment to get rid of money in politics.

LISA DESJARDINS: Stevens has responded, as we saw at the regional Chamber of Commerce in Lansing.

REP.

HALEY STEVENS: We're in a moment of reckoning.

And it's cheap shots to say, oh, well we can't have nice things because of this and that, a super PAC, which yes, that's garbage that we have this dark money.

LISA DESJARDINS: You said very clearly, and you have been clear.

You want to reform.

You don't -- campaign finance reform.

Why not tell super PACs not to use your name?

Why not openly reject the dark money and outside money that's helping you?

REP.

HALEY STEVENS: Well, the Republicans certainly wouldn't be listening to that.

LISA DESJARDINS: So, two wrongs make a right?

REP.

HALEY STEVENS: I'd love to tell the Republican super PACs not to donate -- or not to do a super PAC.

LISA DESJARDINS: Stumping for Stevens is Zach Nessel.

He's secretary of the state Democratic Jewish caucus and the son of the state's attorney general.

He says the AIPAC focus is misguided.

ZACH NESSEL, Haley Stevens Supporter: They support her because she supports Israel and she always has been.

It's not that she owes them anything.

It's that she has been -- their values are aligned.

LISA DESJARDINS: This divide isn't new.

But Democrats criticizing Israel and those pushing left are notching up recent gains, like Democratic Socialist Zohran Mamdani's win in New York City.

Here in Michigan, a recent poll shows El-Sayed with a 16-point lead over Stevens, winning big with independents likely to vote in the race.

MATT GROSSMANN, Michigan State University: They open, like all, with us.

LISA DESJARDINS: Matt Grossmann is a political science professor at Michigan State and co-owns Hooked, a bookstore in Lansing.

MATT GROSSMANN: Democrats are competitive now in Texas, in Iowa, in Alaska, in Ohio.

This shouldn't be the competitive state, certainly to determine the outcome of the U.S.

Senate.

But I think Republicans think, regardless of who wins on the Democratic side, they have a chance here.

LISA DESJARDINS: Grossmann also says the general election could get ugly, particularly if Republicans run against El-Sayed, who'd be the first Muslim senator in history.

ALEENA MALIK: He's fighting for what people want.

And so I think that will make people see past the racism and the superficial things like his name and his identity.

LISA DESJARDINS: If Stevens wins, Aleena Malik will probably vote for her over the Republican.

ALEENA MALIK: I think it goes back to kind of choosing the lesser of two evils.

CINDY GROENE: I don't have any real negatives towards Abdul, but I would like to see him hold another elected job before he made a huge move to the Senate.

LISA DESJARDINS: But, even so, Stevens supporter Cindy Groene says she will definitely vote for El-Sayed if he is on the fall ballot.

CINDY GROENE: My concern is both sides, Abdul supporters, Haley supporters, will not vote for the other if they win.

And that would not result in the Democrats retaining this Senate seat.

LISA DESJARDINS: This is a classic Michigan hard political fight, a test of Democrats' divide and their ability to quickly reunite.

For the "PBS News Hour," I'm Lisa Desjardins in Lansing, Michigan.