Standing on the arch of the Edmund Pettus Bridge in Selma, Alabama, to commemorate the 59th anniversary of Bloody Sunday, Kamala Harris said she felt compelled to begin her remarks by addressing the deteriorating humanitarian catastrophe in Gaza.

“People in Gaza are starving. The conditions are inhumane. And our common humanity compels us to act,” the vice-president said, then stated: “Given the immense scale of suffering in Gaza, there must be an immediate ceasefire.” Loud, sustained applause followed, before she added, after a pause: “For at least six weeks.”

The remarks, the White House was quick to note, echoed Joe Biden’s comments to a reporter days earlier and they reflected the administration’s current efforts to broker a temporary break in Israel’s offensive, to allow for the release of hostages and for desperately needed humanitarian aid to enter the besieged territory. Yet many Americans furious with Biden for his alliance with Israel heard from Harris what they felt has been lacking from the president.

There was an urgency to her speech – delivered in the footsteps of civil rights marchers who were trampled, tear-gassed and beaten with whips and billy clubs as they attempted to cross the bridge – that resonated. The setting seemed to acknowledge the youth movement furious with the president that views Palestinian rights as an extension of the racial justice movement. She pointedly criticized Israel for restricting the flow of aid into Gaza and expressed compassion for the Palestinian civilians living amid the rubble on the brink of famine.

As the 2024 general election contest begins, Harris has emerged as an emissary to the Democratic voters who have soured on Biden since propelling him to the White House in 2020. Over the last several months, she has embarked on a full-scale national tour to highlight the threats to reproductive rights posed by a second Donald Trump administration – an issue that Biden has been criticized for shying away from. Now, as Harris adopts a more forceful tone on Gaza, she is also becoming a leading voice on Middle East diplomacy.

Both issues are poised to play a significant, if not decisive, role in the November general election. Polling shows an erosion of support among core Democratic constituencies amid widespread disillusionment with the economy, concern over Biden’s age and fury on the left at the administration’s handling of the war in Gaza.

For Democrats, reminding voters about the threat Republicans still pose to abortion rights may be the best way to energize young people while winning over independents and suburban women. Outrage over Roe was credited with halting the promised “red wave” of Republican victories in the 2022 midterms; abortion-related ballot referendums have also repeatedly triumphed even in traditionally red states like Kansas, Kentucky and Ohio.

But Harris has her work cut out for her. Like Biden, Harris has been viewed unfavorably throughout much of her tenure.

Antonio Arellano, a spokesperson for NextGen, a national youth-focused nonpartisan voter registration and education program, called the 59-year-old Harris a “liaison” between the administration and the parts of the Democratic base that were critical to Biden’s 2020 victory but hold reservations about him now. With her college campus tour and her reproductive rights tour, he said, Harris has helped elevate issues that are top of mind for young progressives and multiracial voters.

“She brings an energy of vigor and excitement to the election that I think young people can really gravitate to when perhaps enthusiasm lacks elsewhere,” Arellano said.

Harris leapt into the US abortion wars within a day of the leak of the US supreme court decision overturning Roe v Wade.

At a May 2022 speech at a conference for Emilys List, which works to elect Democratic women who support abortion rights, Harris gave a fiery speech where she repeatedly asked: “How dare they?”

“How dare they tell a woman what she can and cannot do with her own body?” Harris asked. “How dare they try to stop her from determining her own future? How dare they try to deny women their rights and their freedoms?”

Harris had spent the first several months of her vice-presidency frustrated by headlines about her apparent lack of direction, staff departures and unforced errors. Allies and experts have long seen sexism and racism in the public scrutiny of Harris, who is the first woman and the first woman of color to hold nationally elected office. The criticism seemed particularly unfair, they said, given that vice-presidents are historically overlooked.

“I’m not saying that there shouldn’t have been any attention paid to management, especially when you see high-profile kinds of departures and hires,” said Andra Gillespie, an associate professor of political science at Emory College. “But I think that there’s still also the question of whether or not people have paid more attention to her, and also whether or not the public has had a more visceral reaction to her because of her race and gender.”

But when it came to the fight over reproductive rights, Harris’s gender, race and age and experience as a prosecutor combined to give her the edge of authenticity that Biden lacks on an issue that is increasingly critical to voters. Many of the 16 states that have enacted near-total post-Roe abortion bans do not have exceptions for rape or incest, a state of affairs that Harris has called “immoral”.

“As a woman on the ticket and the first woman VP and a woman of color, and then secondly, as an AG, she is strongest when her profile is fighting and prosecuting the case. People really like her in that mode,” said Celinda Lake, a Democratic Party strategist and a lead pollster on the 2020 Biden campaign. “She’s so comfortable saying the word ‘abortion’. She’s so comfortable leaning in and speaking to the repercussions.”

Emilys List, which first endorsed Harris 20 years ago when she was elected as San Francisco’s district attorney, has previously committed to spending more than $10m on bolstering Harris in the 2024 elections, according to reporting from Politico; Jessica Mackler, the new president of Emilys List, said that nothing about their plan to support Harris has changed. “Supporting the vice-president is a huge part of our electoral priorities,” Mackler said.

Compared to his running mate, Biden’s recent record on abortion is far more spotty. A devout Catholic, Biden has said that he is “not big” on abortion and, in Thursday’s State of the Union address, spoke at length about the procedure without ever referring to it by name. Instead, he talked of the importance of “reproductive freedom” and promised to “restore Roe v Wade as the law of the land”.

When it comes to the Israel-Gaza war, Harris has begun to take a more visible role, and it appears that here, too, she may be pushing just beyond Biden’s comfort zone.

NBC News reported that the National Security Council toned down parts of Harris’s Selma speech that were “harsher” on Israel. The vice-president’s office denied that her speech had been watered down.

On the Monday after her remarks, Harris met with Benny Gantz, a member of Israel’s war cabinet who had traveled to Washington against the wishes of Prime Minister Benjamin Netanyahu. As she walked into the meeting, Harris denied that there was any daylight between her and the president on the conflict.

“The president and I have been aligned and consistent from the very beginning,” she said.

Many anti-war activists said Harris’s remarks on Gaza were too little, too late. Yet others saw it as a sign of progress – that their pressure campaign was having an impact. Nearly 100,000 Democrats in Michigan voted uncommitted in the primary, which was held just days before her remarks.

“They’re feeling the pressure, and we want them to feel that pressure,” said Khalid Omar, who organized on behalf of the “uncommitted” campaign in Minnesota. “We want them to know that this is unacceptable.”

Biden and Harris’s first joint campaign event of 2024, a rally in Virginia, was meant to focus on reproductive rights – but it was instead derailed by anger over the conflict in Gaza. After Harris and a Texas woman who had been denied an abortion spoke about the importance of defending the procedure, Biden took the stage. He was almost immediately interrupted by a protester who yelled: “Genocide Joe, how many kids have you killed in Gaza? … Palestine is a feminist issue!”

That protester was removed from the auditorium. Another soon cried out: “Israel kills two mothers every hour!”

Observers of Harris’s vice-presidency say the recent attention is recognition of the work she has been doing for months – both on domestic and foreign policy issues.

“To the extent that she has found her voice, it’s because people are finally listening,” said Donna Brazile, a Harris ally and veteran Democratic strategist who teaches women’s and gender studies at Georgetown University.

Last month, Biden dispatched Harris again, this time to the Munich Security Conference, where her mission was to reassure American allies rattled by Trump’s attacks on Nato. There she met with Ukrainian president Volodymyr Zelenskiy and with Yulia Navalnaya, the wife of the Russian opposition leader Alexei Navalny, hours after news broke of her husband’s death in an arctic penal camp.

Less than a week later, she was in Grand Rapids, Michigan, for a stop on her reproductive rights tour. While there, she made a surprise stop at the city’s first Black woman-owned vinyl record shop and purchased a Miles Davis album from the owner, who was thrilled by the visit.

When the Tennessee legislature expelled two Black lawmakers, the White House sent Harris to Nashville, where she joined them in delivering an impassioned plea for gun control. In December, she traveled to Dubai for a UN climate summit, where she juggled wartime diplomacy – delivering at the time the sharpest commentary of any administration official on Israel’s war in Gaza – with climate policy.

“Her vice-presidency has been significant both in terms of her spokesperson role and in terms of a number of significant and highly visible diplomatic assignments that President Biden has given her,” said Joel Goldstein, a historian of the US vice-presidency.

There is, however, another reason why scrutiny of Harris may be intensifying: her running mate’s age.

If he wins a second term, Biden would turn 86 before leaving office. A New York Times and Siena College survey found that 73% of registered voters believe Biden is “just too old” to be an effective president. The poll was conducted more than two weeks after a special counsel described him as a “well-meaning, elderly man with a poor memory” and “diminished faculties in advancing age.”

“The age of both Biden and Trump will focus more attention on the vice-presidential candidates,” Goldstein said.

Republicans have sought to leverage concerns about Biden’s mental and physical health against Harris, casting her as an unsteady lieutenant ill-prepared to assume the presidency. In the weeks before dropping out of the Republican presidential primary, Nikki Haley argued that if Trump were to win the party’s nomination, he would lose to Biden, who would be unable to finish a second term, leading to a Harris presidency. The prospect, Haley said, “should send a chill up everyone’s spine”.

But Harris is leaning in to her leading role. After the State of the Union, she headed west to Arizona, the next stop on her reproductive rights tour. On Saturday she was scheduled to campaign with Latino organizers in battleground state Nevada.

To those who doubt whether the vice-president could step into the presidency, she is blunt.

“I’m ready, if necessary,” Harris told NBC News on Friday. “But it’s not going to be necessary.”

Rachel Leingang contributed to this report from Minneapolis