After more than three years supporting President Joe Biden's policy agenda as his deputy, Vice President Kamala Harris must articulate her own agenda for her presidential campaign -- and the first term that could follow.

Since Biden announced on Sunday that he was leaving the 2024 race, Harris has secured commitments from enough delegates to become the presumptive nominee if they all honor their commitment when voting, according to ABC News reporting.

Now Harris -- who ran well to the left of Biden during her unsuccessful presidential primary campaign in 2020, but has since become a loyal advocate of the administration's policies -- is taking on the challenge of establishing her own path forward and stance on key issues that matter most to voters as the November election approaches.

Her 2020 platform and some remarks from during her vice presidency offer a glimpse of a Harris presidency that could prove more progressive than Biden's in several key areas.

Israel-Gaza

Israeli Prime Minister Benjamin Netanyahu addressed a joint session of Congress on Wednesday, with Harris -- who, as vice president, customarily presides over such proceedings -- noticeably absent.

While Harris' team has said her absence is merely the result of a scheduling conflict and the vice president will meet one-on-one with Netanyahu later this week, she has in recent months signaled that she may take a more stern approach to Israel's war with Hamas in Gaza.

In the wake of the Oct. 7 Hamas attack on Israel, Harris was initially a strong supporter of Israel's right to defend itself against Hamas -- knocking down a suggestion that the Biden administration might condition aid to the country in November, saying "we are not going to create any conditions on the support that we are giving Israel to defend itself."

But by December, Harris began wading deeper into Middle Eastern diplomacy during a trip to Dubai for a United Nations climate conference where she also met with leaders from the region. During the trip, she took a more forceful tone with Israel than many other senior administration officials had done at the time, declaring "too many innocent Palestinians have been killed" and saying the administration believes "Israel must do more to protect innocent civilians."

In a March address in Selma, Alabama, marking the anniversary of Bloody Sunday, Harris called out Israel again -- saying its government "must do more to significantly increase the flow of aid -- no excuses" and calling on Israel to open border crossings and ensure humanitarian workers were not targeted.

In an interview published earlier this month in The Nation, Harris said young Americans protesting the war in Gaza are "showing exactly what the human emotion should be" and that while she "absolutely rejects" some of their statements, she understands "the emotion behind it."

And she's been vocal in her support of an at least temporary cease-fire, saying during her March speech in Selma that "given the immense scale of suffering in Gaza, there must be an immediate cease-fire" for at least six weeks.

Harris doesn't have a long-standing relationship with Netanyahu in the same way Biden does, but she met with Israel's Benny Gantz at the White House while he was serving on the country's war cabinet in March. She also met with Israel's President Isaac Herzog earlier this year on the sidelines of the Munich Security Conference.

Abortion

Already the administration's lead messenger on the central campaign issue of abortion rights, Harris has been consistently more boldly outspoken on the issue than Biden.

Before running for president in 2020, she went after crisis pregnancy centers as California attorney general and went viral for a line of questioning with then-Supreme Court nominee Brett Kavanaugh, where she pressed him to name a single law that polices what men can do with their bodies.

Her 2020 platform included a proposal to pass a Reproductive Rights Act that would have taken affirmative steps to enforce Roe v. Wade, which the Supreme Court later overruled in 2022.

Since the Supreme Court's decision affecting Roe, Harris has toured the country as bans went into place. She made history by being the first vice president to ever visit an abortion clinic in March -- a move that demonstrated how loudly supportive of abortion rights she is -- and delivered a fiery speech on then-GOP presidential candidate Ron Desantis' home turf in Florida this spring when a six-week ban went into effect there.

She made it clear in her first rally on Tuesday that abortion rights would continue to be a central issue for her as a presidential candidate.

"We who believe in reproductive freedom will fight for a woman's right to choose because one does not have to abandon their faith or deeply held beliefs to agree the government should not be telling her what to do," Harris said in a rally in Indiana on Wednesday, addressing the Zeta Phi Beta sorority.

That's not to say Biden didn't also make abortion rights a central tenet of his administration and campaign, said Mary Ziegler, a professor of law at University of California, Davis and abortion historian. However, she said, he was constrained by generational and religious differences that made Harris "the much more effective, passionate messenger on reproductive issues."

Should Harris win in November, "I think there would be some differences in substance, really significant differences in tone, and then, maybe or maybe not, differences in outcome," Ziegler said.

Outcomes -- such as codifying Roe vs. Wade into law, going even further to also protect birth control or in-vitro fertilization, or pursuing further legal challenges to protect abortion rights -- would depend primarily on how Democrats perform down the ballot in November and whether Harris has the opportunity to confirm any more justices to the Supreme Court.

Health care

In her remarks to campaign staff Monday, Harris said that her campaign will "fight to build a nation where every person has affordable health care."

The Medicare for All plan that Harris proposed in 2020 would have covered all medically necessary services, including emergency room visits, doctor visits, vision, dental, hearing aids, mental health and substance use disorder treatment, and comprehensive reproductive health care services. The plan had a 10-year transition period.

Under Harris' plan, Americans would have had a choice between the public Medicare for All plan and plans from private insurers that would have had to adhere to strict Medicare requirements on costs and benefits.

To pay for the program, she proposed charging an additional premium to households making above $100,000 per year, with a higher income threshold for those in higher-cost-of-living areas.

In 2020, Biden called for a less ambitious "Medicare for all who want it" public option plan. However, according to Roll Call, he hasn't mentioned that public option since December of 2020 -- before he took office.

Biden also previously suggested he would veto a Medicare for All bill, arguing that it would raise taxes for the middle class.

But the vice president's past policy differences with Biden may not mean all that much for a Harris presidency.

"I wouldn't expect it to change at all [from Biden's agenda]," David Barker, a professor of government at American University, said. "Until there's some indication that that's politically realistic, I don't think anybody's going to even try."

Barker added that smaller changes, similar to the $35 price cap on insulin for seniors on Medicare in the Inflation Reduction Act, is "the way they'll continue" in a Harris administration.

Criminal justice

While Harris faced sharp criticism from the left during the 2020 primary for her background as a prosecutor, her platform that year contained a slate of ambitious reforms to the criminal justice system aimed at ending mass incarceration and fighting racial inequities.

Harris' platform advocated to legalize marijuana and expunge some marijiuana-related convictions; end cash bail and mandatory minimums; eliminate the sentencing disparity between crack and powder cocaine; and stop the use of private prisons and the death penalty.

Her criminal justice plan also sought to increase the Department of Justice's oversight of police departments and limit them from acquiring certain kinds of military equipment. In a clip that has been circulated by Republicans, she also advocated for restoring the right of formerly-incarcerated people to vote and automatically expunging non-serious, non-violent offenses after five years.

The Biden administration's most significant action on criminal justice came when it took action on marijuana, reducing federal criminal penalties for offenses relating to the drug and pardoning those with criminal charges for simple possession of marijuana.

While Harris' 2020 platform went well beyond Biden's on criminal justice, her recent remarks make no indication that it will be a major theme of her campaign. The issue went unmentioned in her speech at the campaign's Wilmington, Delaware, headquarters on Monday.

ABC News' Shannon Kingston, Anne Flaherty and Nathan Luna contributed to this report.