Last week, Sen. Kamala Harris (D-CA) laid down a marker that's been lost in the intervening crush of news but could prove enormously important in December. She became the first Senate Democrat to publicly vow to oppose any government funding bill unless Congress takes action to protect the 700,000 DREAMers rendered newly vulnerable by President Donald Trump.

“I will not vote for an end-of-year spending bill until we are clear about what we are going to do to protect and take care of our DACA young people in this country,” Harris said at a press conference. "Each day in the life of these young people is a very long time, and we've got to stop playing politics with their lives."

The unexpected move helped cement Harris’s burgeoning reputation as the most outspoken ally of immigration activists on the Hill. Most Senate Democrats, like many Senate Republicans, have promised to push for a deal to protect the DREAMers. But beyond Rep. Luis Gutiérrez (D-IL), few Democrats in Congress have publicly adopted the line of the immigration activists themselves — that the government should be shut down this December without a legislative guarantee that the DREAMers get to stay.

Harris is now the first senator — and certainly the most high-profile politician in the country — to take that demand and make it her own. And both immigrant rights groups and their conservative opponents are taking notice.

“Seeing her do this is another demonstration that she’s modeling the kind of leadership we should expect from other Democrats. We were just so excited,” said Adrian Reyna, director of membership at United We Dream, the biggest DREAMer advocacy organization. “I see her as our new emerging champion in the Senate.”

Others are more skeptical of her motives. “It’s hard not to evaluate this through any lens other than the 2020 presidential primary,” Matt Mackowiak, a Republican strategist and president of the Potomac Strategy Group, told Vox.

But to understand Harris’s new role as the Senate’s leading immigration dove, future elections shouldn’t be your only guidepost. You also need to understand her backstory — both personal and political.

Why immigration issues are deeply personal to Harris

Harris, 53, did not arrive in Washington new to immigration issues. Her mother, Shyamala Gopalan Harris, emigrated from India in 1960; her father, Donald Harris, emigrated from Jamaica in 1961.

Harris lived in Canada from when she was 12 until she was 18. Tracks from the musical Hamilton, which glorifies the American immigrant story, appear on her Spotify playlists. Her “maiden speech” on the Senate floor this January began by imagining her mother, who died of cancer in 2009, looking down from heaven in horror at President Trump’s Muslim ban.

“Knowing my mother, she’s probably saying, ‘Kamala, what on earth is going on down there? We have got to stand up for our values!” Harris said. The first bill she introduced in Congress, the Access to Counsel Act, requires federal officials to let lawyers communicate with immigrants in limbo while trying to reach the US.

Allies of the senator say her formative experience on immigration policy came as California’s attorney general in 2014 — when a surge of unaccompanied minors from Central America posed a new and unique crisis for law enforcement across the country. Almost 30 percent of the migrant refugees settled in California, far more than in any other state in the country.

“The flood of children from Central America had a profound impact on Kamala and her office,” said Daniel Suvor, who served for three years as Harris’s chief of policy in the AG’s office and considers himself a friend. “That’s what’s led, I think, to her more recent national leadership.”

Suvor recalled one story in particular: In June 2014, Harris met with a refugee from El Salvador in her office in downtown Los Angeles. Before fleeing the country, the young woman had seen a friend get shot and killed while the two were sitting on a park bench.

Harris took dozens of meetings like that with immigration nonprofits and migrants themselves, including with pregnant women and women who had fled violent abuse in their home countries. “She took it very personally,” Suvor said. “She'd always cared about immigration, but I really think that experience heightened her attention to the issue.”

How Attorney General Kamala Harris confronted the child migrant crisis

Harris’s public policy work on immigration began as district attorney of San Francisco, when she created free legal clinics in immigrant-heavy parts of the city and started a job training program for ex-convicts that drew scrutiny — and praise — for allowing undocumented immigrants to participate.

But it wasn’t until Harris served as California’s AG that she stepped into the immigration limelight.

The breadth of her work on immigration was vast, by the standards of both supporters and opponents. Harris issued controversial bulletin guidelines to California law enforcement “making clear they could not hold immigrants indefinitely,” Suvor said. She brought high-end California law firms into her AG’s office and connected them with immigration nonprofits. She crafted legislation that put millions of dollars into legal services for the refugees of the child migrant crisis, bringing California state senators into her office to meet with undocumented immigrants. (She’s now pushing similar, if more ambitious, legislation at the federal level.)

Harris also crafted legislation to help ensure that California law enforcement gives immigrants who step forward to report or testify about crimes “u-visas,” which shields them from deportation for doing so. “[The law] will help prosecutors obtain convictions while strengthening the relationship of trust between law enforcement and immigrant communities,” Harris said at the time. She personally helped write California’s brief in US vs. Texas, the case over the constitutionality of the Deferred Action for Parents of Americans program that made it to the Supreme Court.

Critics of Harris and lenient immigration policies allege that her positions amount to amnesty and protections for those who have, by definition, committed crimes. “Her record on immigration policy is siding with people who are coming into the country illegally and obstructing enforcement of immigration laws that preserve job opportunities for Americans,” said Jessica Vaughn, director of policy studies for the Center for Immigration Studies, in an interview.

In particular, immigration hawks like President Trump have cited a 2015 murder in San Francisco committed by an undocumented immigrant allegedly freed because of the sanctuary city policies pushed by Harris. “She was giving license to enact sanctuary policies at the local level that resulted in presentable public safety problems,” Vaughn added. “That’s a curious thing for the state’s top law enforcement official to do.”

But there’s no doubt from either critic or ally that it’s central to her work as a politician. Valerie Jarrett, who served as a senior Obama White House adviser, even set up conference calls in which Harris explained the policies spearheaded in her office to state attorneys general across the country.

“She has a real-world understanding of how immigration policy intersects [with] criminal justice policy on the ground,” Suvor said. “This stuff is personal to her. She really is an expert on the issues.”

As a senator, Harris has built a bridge to Latinos and immigration activists

In Washington, activists say Harris has spent an almost certainly unrivaled amount of time among senators advocating for the DREAMer cause — taking meetings, holding rallies at the Capitol and in her state, and meeting with California DACA recipients at risk of deportation.

“There’s been no new voice on this issue more electrifying than hers, particularly for firing up the grassroots,” said Ben Wikler, the Washington director of MoveOn.org. “Harris was the first Senate Democrat to say exactly what activists and those terrified by the threat of deportation for DACA recipients have been waiting to hear.”

Shortly after the 2016 election sent both Trump and Harris to Washington, staffers at the Coalition for Humane Immigrant Rights of Los Angeles (CHIRLA) talked with Harris’s team. The California Democrat wanted her first press conference as a senator-elect to be with CHIRLA, and to focus on the need to defend immigrants.

Two days after Election Day, Harris stood by the podium as a mother explained in Spanish why she feared deportation. Activists by her side chanted, “Si, se puede!”

“I’ve worked with many elected officials and heard many promises, but this was the first time I heard an elected official show up and be there and not shy away after their race was over,” Polo Morales, political director for CHIRLA, told me. “She’s been checking in with immigrant rights groups regularly.”

Harris’s first big moment in the immigration spotlight as a senator came in January, when she sparred with John Kelly, then Trump’s nominee for Department of Homeland Security and now his chief of staff. Harris wanted to know whether Kelly would vow not to share DHS information on DACA recipients with Immigration and Customs Enforcement (ICE). Kelly struggled to answer.

Under Harris’s questioning, Kelly looked visibly taken aback multiple times. At one point, he said, “Let me at least finish once before you interrupt me.” On two more occasions, he would ask, “Will you let me finish?”

Headlines from the exchange ricocheted across the web. Immigration activists were thrilled.

On August 28, as rumors began swirling that Trump would rescind DACA, Harris held a roundtable discussion with about eight DREAMers to highlight their plight. On September 5, Trump announced he would end the DACA program. Harris held a press conference on DACA the next morning, and then a Facebook live event with fellow Senate Democrats on DREAMers. She followed that by tweeting several stories from anonymous DREAMers who fear deportation to her nearly 1 million followers.

The next month proved much of the same. She headlined rallies for the DREAMers outside the Capitol on October 3 and 6. She held another rally at UC Irvine on October 11. She’s met with DREAMers at her DC office and in California on at least a dozen occasions since taking office.

Assistant Democratic Leader Dick Durbin is viewed as the most tireless supporter of the DREAM Act inside the Capitol, whipping Senate Republicans to support his bill, according to activists. But Harris has been the lead champion of drumming up external public pressure.

“She's had a lot of face time with undocumented youth, and that has translated to her really championing the issue of immigration in a way we haven’t seen in a long time,” Morales said.

All of Harris’s work could pay huge 2020 political dividends

It’s not surprising that the Senate’s strongest immigration advocate comes from California, where the local Republican Party has been all but decimated. This November, Harris didn’t even have a Republican general election opponent because no GOP contender could come in second and advance through the state’s top-two primary system.

And the particular circumstances of the California GOP’s collapse make Harris’s immigration position even more likely. Pete Wilson, the state’s former governor, embraced a brand of nativist immigration politics that made the Republican brand toxic in the rapidly diversifying state.

But the politics of her immigration stand could boost Harris nationally as well. Within hours of her announcing that she was adopting activists’ positions on the government shutdown, the Latino Victory Fund sent out an email blast to its thousands of supporters asking for donations. They heralded Harris’s position as “amazing” and proclaimed, “¡La lucha sigue!” — “the fight continues.”

Harris and her team are quick to cut off any discussion about her 2020 presidential aspirations. (“Oh, God,” she said when New York Times reporter Matt Flegenheimer approached her about the subject at a congressional softball game.) But whether or not she’s running for national office, there’s ample reason to believe she’s created a large and powerful constituency among Latinos who care deeply about the DREAM act and federal immigration policy — particularly with her latest position on DACA recipients.

“All these Senate Democrats are beating around the bush, but Harris came out very publicly and very explicitly about tying her vote on the spending bill to a fix for DREAMers,” said Angel Padilla, policy director of Indivisible. “It’s a huge deal, and I don’t understand why more Democrats aren’t doing this. If you really cared about DREAMers, you have to do this.”

As talk of her 2020 potential increases, Harris has faced some criticism from her left flank. The Week’s Ryan Cooper wrote an article comparing her to Sen. Cory Booker (D-NJ) and former Gov. Deval Patrick (D-MA), and argued that she was “being groomed by the centrist establishment.” Paste Magazine's Jason Rhode has similarly called her a "creation of the financial sector which funds the Democratic Party," as well as a "protector and servant of the carceral state," a reference to her time as a prosecutor.

This weekend, Harris was scheduled to appear at a private fundraiser with Sen. Sheldon Whitehouse (D-RI), and has also appeared at donor functions in the Hamptons — routine behavior for national Democrats, but behavior that some on the left also claim will compromise her ability to challenge the moneyed classes and special interests.

But Harris is also savvily positioning herself to endear herself the party’s base. Late this August, she became the first Senate Democrat to embrace Sen. Bernie Sanders’s (I-VT) single-payer health care plan. According to multiple reports, she’s generated tremendous excitement among black lawmakers as a presidential hopeful. Embracing the DREAMers’ cause could help solidify her left-wing bona fides among another crucial constituency for a potential internal Democratic Party race.

“It’s a win-win for her: If protections for DREAMers are in the deal, she can take credit for it. If it’s not, she can vote no and establish herself for the 2020 primary as a leader on the DREAMer issue, which is very important to the Democratic base,” said Mackowiak, the Republican strategist.

In her stump speech, Harris likes to note that close to half of Californians either are immigrants or have at least one immigrant parent.

Many of them are watching her.

“It can feel so easy to walk away from our fight, which can feel so exhausting,” said Reyna, of United We Dream. “But it’s really so refreshing to hear about Kamala. It suggests all hope is not lost.”