The vote was overwhelming: 420 to one. The sole dissenter was Representative Barbara Lee, a California Democrat.

On Tuesday, Lee — at the age of 77 — will face possibly the greatest electoral test of her career when California holds a primary for its open Senate seat.

The congresswoman is running in that race on her credentials as an antiwar candidate. This time, however, her focus is on achieving a ceasefire in Gaza — a position she says distinguishes her from the rest of the field.

Lee is in competition against more than 20 other candidates, including prominent Democratic representatives like Adam Schiff and Katie Porter. The stakes are high: Schiff, Lee and Porter have all opted not to run for reelection in the House, in order to focus on their Senate prospects.

That means this year’s Senate primary could deal Lee her first electoral defeat in 26 years. But her candidacy shines a light on the range of Democratic views towards Israel’s war in Gaza — a spectrum that could translate into fractures as the party seeks unity at the ballot box.

For me, doing what’s right is leadership.

The lone vote against the War in Afghanistan then.

California’s only US Senate candidate calling for a permanent, unconditional ceasefire now.

Please vote for me, Barbara Lee—the peace and security candidate—by tomorrow, Tuesday! pic.twitter.com/uFcBCJMdd2

— Barbara Lee (@BarbaraLeeForCA) March 4, 2024

A beacon for progressives

Amar Shergill, the chair emeritus of the California Democratic Party Progressive Caucus, is among those supporting Lee’s Senate bid.

He told Al Jazeera that Lee’s stance on Israel’s war in Gaza was among the reasons he publicly backed her campaign. “Barbara Lee is a voice to end suffering around the world, regardless of the political cost, and she will fight for it,” he said.

Over the past months, Lee has reiterated her call for a ceasefire in Gaza dozens of times on her social media accounts, making it a defining element of her campaign.

Americans — and specifically Democrats — have increasingly voiced concern about the dire conditions in Gaza, where Israel has killed more than 30,000 Palestinians.

A February poll from the Associated Press and the NORC Center for Public Affairs Research found that half of Americans felt Israel had “gone too far” in its military campaign. That number, however, shot up to 62 percent among Democrats alone.

But many mainstream members of the Democratic Party have long resisted calls for a permanent ceasefire, instead affirming support for Israel’s military offensive. They include President Joe Biden, who has only recently articulated hopes for a ceasefire to pause — though not definitively end — hostilities.

Lee’s supporters hope that her stance on the issue will carry her to a shock victory on Tuesday. Public opinion polls show her trailing her Democratic rivals Schiff and Porter, as well as Republican contender and former baseball player Steve Garvey.

Foreign policy is rarely a top priority at the ballot box, but Shergill said voters are increasingly drawing parallels between injustices in Palestine and inequality at home.

“The youth is inspired by her moral clarity. We see immigrant communities who understand that what’s happening in Palestine could happen to their relatives in ancestral homes around the world,” Shergill told Al Jazeera.

California’s ‘jungle’ primary

The Senate race in California — the state with the largest population in the country — is scheduled to arrive on Super Tuesday, a crucial date in the US electoral calendar. More states hold primaries on that date than on any other.

Adding to the scrutiny of that high-profile occasion is the symbolism behind this particular Senate race. Lee and the other Senate hopefuls aim to fill a seat long held by the late Senator Dianne Feinstein, a key Democrat who died in 2023.

Feinstein held the title of longest-serving female senator in the history of the US Congress. After her death, California Governor Gavin Newsom appointed Laphonza Butler to serve the rest of her term.

But Butler has declined to run in the 2024 election, leaving the Senate race without an incumbent. An open Senate seat in California, a Democratic stronghold, is a rarity. Whoever wins will spend a six-year term in Congress.

Most states have partisan primaries, where candidates from different parties compete on separate slates to claim their party’s nomination for the general election.

But California holds what is known as a “jungle primary”: Candidates, regardless of political party, compete together in the first round of voting and the top two vote-getters face off in the general elections.

So a Democrat like Lee not only has to compete against members of her own party but Republicans and independents as well.

The candidates

Garvey, the Republican baseball star, has led a dark-horse campaign that has stunned political observers. Several polls show him in a tie with — or surpassing — Porter for second place.

But even if Garvey makes it to the general elections, Democrats are widely expected to retain the Senate seat in November.

Schiff, an ally of former House Speaker Nancy Pelosi, is currently leading the race. Considered a favourite of the party establishment, Schiff developed a national profile after he led an impeachment inquiry into then-President Donald Trump in 2019.

Porter, meanwhile, is a left-wing lawmaker who rose to prominence with her consumer advocacy and criticism of major corporations.

On domestic issues, Lee, Schiff and Porter share similar views, albeit with different approaches. Even Schiff — who is considered the centrist in the race — supports progressive priorities like universal healthcare and the Green New Deal climate plan.

But the war on Gaza is a critical point of divergence. Schiff, the former chair of the House Intelligence Committee, is a staunch defender of Israel. Last month, he voted with the Republican majority in favour of a $17.6bn aid bill for Israel. Most Democrats had opposed the measure, which ultimately failed, because it did not include assistance for Ukraine.

Porter, who has been in Congress since 2019, is not known for her foreign policy positions but is also a vocal supporter of Israel. In December, she called for a ceasefire with a caveat: that Hamas be removed “from operational control of Gaza”.

In the same statement, Porter falsely blamed Hamas, not Israel’s blockade, for the “shortages of food, clean water, fuel and medicine” over the years in Gaza.

“I believe we need a lasting ceasefire,” she recently told the Los Angeles Times. “This is a conflict between Israel and Hamas, and the job of the United States is to bring Israel and Hamas into conversation and to find out what the preconditions are, like the release of hostages and different leadership in Gaza.”

In contrast, Lee has been consistently calling for an immediate and unconditional ceasefire.

“The only way that we’re going to see peace and security and justice for the Israelis and the Palestinian people is through a political and diplomatic solution,” Lee said in November 2023.

The congresswoman has also been endorsed by prominent progressives who are supportive of Palestinian rights, including Congress members Cori Bush, Ilhan Omar, Ayanna Pressley and Mark Pocan.

Still, she has struggled to keep up with the fundraising of Schiff and Porter, who enjoy more institutional support. Filings made with the Federal Election Commission show that Schiff, for instance, had nearly $34.9m in “cash on hand” for his campaign in January.

Lee’s chances

So does Lee have a chance in the Super Tuesday race?

Yassar Dahbour, the chair of the Palestine American League, says he is “hopeful” but realistic about her chances.

“She stood out there, and she’s resonating with the voters, but there are other factors in effect,” Dahbour told Al Jazeera. “And unfortunately, in American politics, money has quite an effect on the result and outcome of elections.”

Dahbour lauded Lee’s advocacy for a permanent ceasefire in Gaza, calling her a voice for justice, but said it remains to be seen how much her position will sway voters beyond the progressive base.

For his part, Shergill dismissed polls that show Lee behind the three other major candidates, saying that early signs point to a low turnout on Tuesday.

“In a low turnout election, the kind of energised folks who want to see Barbara Lee elected could make the difference,” he said.