The St. Louis County prosecutor challenging Representative Cori Bush for her House seat in Missouri began his day Thursday being interviewed by a prominent Black radio personality in St. Louis.

The prosecutor, Wesley Bell, then went on to lecture a sociology class at St. Louis Community College, where he once taught criminal justice, had lunch at a soul food restaurant in Ferguson, peaceful now nearly a decade after protests there practically created the Black Lives Matter movement.

He met that afternoon with laborers’ unions, stopped by a Vietnamese community celebration of the Lunar New Year, and ended well into the night at the North County Democrats Club, in suburban Hazelwood.

“If you call me, I’m going to pick up,” Mr. Bell, 49, assured members of the Laborers’ International Union of North America, whose leaders once endorsed Ms. Bush and now back her challenger, Mr. Bell. “And if you want me to show up, I’m going to show up.”

Driven by the passions surrounding the massacre of Israelis on Oct. 7 and the ensuing war in Gaza, pro-Israel groups are financing a slew of primary challenges in heavily Democratic districts, aimed at unseating outspoken critics of Israel on the political left.

The deadly war has divided centrist Democrats from progressives like Ms. Bush, who has condemned Israel for its response, seeking to hold up aid while pressing for a cease-fire as the death toll in Gaza has mounted. Late last month, Ms. Bush and the House’s only Palestinian American, Rashida Tlaib, were the lone opponents of a resolution to bar Hamas members and those who participated in the attacks against Israel on Oct. 7 from the United States.

But unlike many of the primary contests fueled by various groups — like the American Israel Political Affairs Committee; its political affiliate, the United Democracy Project; and the independent Democratic Majority for Israel — the Bush vs. Bell battle in Missouri’s First District pits progressive against progressive, each with a considerable record to run on that has little to do with Israel.

And though driven by money from pro-Israel groups and firm Israel critics, the fight over Missouri’s deep blue First District is likely to hardly mention the Middle East. Instead, it will be a battle over representation, and what that should look like for troubled St. Louis.

“I’m being targeted by AIPAC because not only do I believe Palestinians deserve to live freely and peacefully just like Israelis, but because I want to protect our democracy from Republican extremism,” Ms. Bush said Monday. “I want to codify abortion rights, I want to pass meaningful gun violence prevention legislation, and I want to raise taxes on billionaires — all things AIPAC, their G.O.P. donors, and the insurrectionists they endorse, oppose.”

Ms. Bush is an icon of the left, an activist from the streets of the Ferguson protests who took her voice to the halls of Congress. But Mr. Bell was on those streets as well, mediating between the demonstrators and the police, and then being elected to the Ferguson City Council.

He is a key figure in the progressive prosecutors movement, having spent nearly a decade trying to steer low-level offenders from incarceration to mental health and drug treatment programs, to free the wrongfully convicted from St. Louis prisons, and to increase scrutiny of official misconduct in law enforcement and public prosecution.

The primary is expected to draw national attention because of broader discussion of Israel and how much the Democratic Party is willing to accept the Jewish state’s harshest critics, such as Ms. Bush. But in the city of St. Louis and the surrounding county that shares its name, the race may revolve around the limits of activism and personality in a region sorely in need of tangible help.

Ms. Bush enters the race as a lightning rod. Her pro-Palestinian activism has made her a singular focus of pro-Israel groups. She has acknowledged a federal criminal investigation into the use of campaign funds to pay her husband for security work. And her outsize personality has rubbed some in Democratic leadership the wrong way.

But to Mr. Bell and his supporters, her infractions are more local. First and foremost, she voted against the bipartisan infrastructure bill, a slap to the unions that had backed her. Worse still, she never met with them to explain her vote, said Clinton McBride, the government affairs director of the Laborers’ International Local 110.

“Communication is nice,” he said. “It says a lot when there isn’t any.”

Ms. Bush denied that she had left unions in the dark, contending that her team was in touch before, during and after the vote.

There are plenty of voters in St. Louis who love Ms. Bush’s in-your-face style of activism, and lament having to choose between two progressives. Ken Hughes, a retired member of the laborers’ Local 42, recalled how in 2021 Ms. Bush camped out on the steps of the Capitol in an orange sleeping bag and a lawn chair, a vigil that forced the extension of a pandemic-era moratorium on evictions.

“She’s a fighter for the people, and I like that,” said Mr. Hughes, 60, who has not decided how he will vote in the Aug. 6 primary.

His friend, Greg Lomax, 54, had been undecided at the beginning of Thursday’s labor meeting. But then, he said, “I just learned today that she voted against the infrastructure bill.”

Mr. Lomax spoke approvingly of her convictions, adding with a tone of frustration, “but she’s so, you know, resistant.”

Megan Green, president of the St. Louis City board of aldermen, said that Ms. Bush has been attuned to the city’s needs. Ms. Bush, she said, has secured nearly $2 billion for St. Louis community health care facilities, public schools and nonprofits.

“For those of us who live here, when Cori says your congresswoman loves you, our community feels it,” Ms. Green said.

Pro-Israel groups have yet to formally intervene in the primary race, but an AIPAC official said Monday that the group has endorsed Mr. Bell. Other organizations are expected to endorse Mr. Bell soon. At the same time, the fund-raising of those groups since Hamas’s Oct. 7 attack on Israel and the resulting war in Gaza has been staggering.

The United Democracy Project announced receipts of more than $44 million by the end of 2023, with almost $41 million still in its war chest. Among its contributors were well-known pro-Trump Republicans, such as Bernard Marcus, the co-founder of Home Depot, who gave the political action committee $1 million.

The Democratic Majority for Israel has $1.7 million more to spend at year’s end.

Those groups are targeting a number of incumbent Democrats this cycle, including Representatives Summer Lee in Pittsburgh, Ilhan Omar in Minneapolis, Jamaal Bowman in New York and Ms. Tlaib in Detroit.

“Beating an incumbent member of Congress is the hardest thing in politics; that’s just a statistical fact, and she is not an unpopular politician,” said Mark Mellman, a veteran Democratic operative and the founder of the Democratic Majority for Israel PAC.

But, he added, “She can be beaten.”

Marcy and Richard Cornfeld, the co-chairmen of the St. Louis AIPAC Council, have already given Mr. Bell the maximum, as has the financier Tony Davis. Timothy Drury, a scion of a Republican hotelier family, has maxed out his contributions to Mr. Bell. So has Reid Hoffman, the LinkedIn founder and Democratic megadonor.

It is telling that Mr. Bell considered a run for the Senate against Missouri’s senior senator, the Republican Josh Hawley, only to reconsider, said Usamah Andrabi, a spokesman for Justice Democrats, the left-wing political action committee that backed Ms. Bush’s rise and will back her again this year.

“Wesley Bell went from running against Josh Hawley, an actual right-wing insurrectionist, to taking thousands of dollars from the donors of Josh Hawley, Donald Trump and almost the entire Missouri Republican delegation to run against Missouri’s first Black congresswoman,” he said.

To Ms. Bush and liberal activists, locally and nationally, such contributors are disqualifying to a candidate who insists he is the progressive champion of local issues.

“I don’t see Wesley Bell as a progressive,” said Hannah Rosenthal, co-founder of Progressive Jews of St. Louis and a Bush ally. “His allegiance with AIPAC supporters is a prime example.”

Ohun Ashe, an activist who met Ms. Bush during the 2014 street protests in Ferguson after the killing of Michael Brown, said the impending intervention of national pro-Israel groups was part of a pattern of posturing for Mr. Bell.

Mr. Bell helped mediate between protesters and Ferguson police during the unrest, and then in 2018, he beat the longtime incumbent county prosecutor, Robert McCulloch, on a promise to reopen the case against the police officer who shot Mr. Brown, Darren Wilson.

He kept that pledge, and then in 2020 said he could not build a sufficient case against the officer, the same conclusion reached by his predecessor and the Department of Justice.

Even supporters of Mr. Bell say the sting lingers.

“Some of the people who put him into office as prosecutor might not be supporting him against Cori Bush,” said Ferguson’s current and first Black mayor, Ella Jones, who does back him. “They’re still upset.”

Mr. Bell, in an interview said it was pretty rich for Ms. Bush and her supporters to question a primary challenge backed by outside money, since Ms. Bush did just that in 2020, defeating a 10-term incumbent, William Lacy Clay Jr., whose family name was practically synonymous with Missouri’s first district.

Mr. Bell readily offers up views appealing to pro-Israel donors, saying Israel has a right to self-defense, and castigating Ms. Bush for some of her votes, especially her opposition to U.S. investments in Israel’s Iron Dome missile defense system, which he calls critical to stopping a wider war in the Middle East.

But his campaign centers on his record: 2,200 low-level, nonviolent defendants diverted to health care, job-training and mentoring programs, with a recidivism rate of 5.9 percent; the establishment of a unit to investigate credible allegations of wrongful imprisonment and official misconduct; and an end to death penalty prosecutions in the county — all pursued amid a national backlash against such efforts.

“That’s a big deal in Missouri,” said Jessica Brand, founder of the Wren Collective, which presses for a less punitive approach to prosecution. “Being committed to that movement over the long term is hard because they come for you.”