If President Joe Biden decides to drop out of the presidential race, it appears likely that his replacement at the top of the ticket would be his running mate, Vice President Kamala Harris.

Until this week, that possibility wasn’t really worth pondering too much. But after Biden’s disastrous performance during Thursday night’s debate, Harris becoming the Democratic nominee is suddenly a more serious hypothetical.

Before considering what that would actually look like, it’s helpful to take stock of her vice presidency — and vice presidential candidacy — so far. Despite frequent criticisms and confusion surrounding what exactly her job is, she is now emerging as an indispensable surrogate and defender, and maybe even successor. She hasn’t been a particularly groundbreaking vice president, but she has had moments on the campaign trail, albeit overlooked by the public and the press, when she is able to showcase her value. It’s a preview of how her role could change in the coming months and even years, whether or not Biden steps aside.

Thursday night was one of those times. As shocked and panicked reactions from Democratic operatives and the political press began to pour in post-debate, Harris was dispatched to defend Biden on CNN and MSNBC. She admitted that Biden had a “slow start,” but rounded that answer off by playing up a “strong finish” by the president. She went on offense: attacking Trump for his many lies during the debate and emphasizing Trump’s statements in defense of the January 6 insurrection and refusal to accept the results of the election.

In the process, she surprised a host of pundits who wondered why the White House has “kept her under wraps for three years.”

The answer is complicated.

Unlike Biden’s tenure under former President Barack Obama, Harris’s role as vice president has been low-key. For most of her term, she’s been relegated to warm-up speaker and occasional Biden stand-in, delivering remarks at White House events with the president, attending summits and visiting foreign leaders when Biden is needed in DC or on another trip, or, like Thursday night, brought in to do clean-up.

Many of those back-seat responsibilities have been due to the nature of the vice presidency: a constitutional office without any clear authorities beyond being a spare body in the event the president can’t do his job and being an extra vote when the US Senate is evenly tied.

But some of it appears to have been intentional. Vice presidents have exerted influence and power before. Vice President Dick Cheney essentially ran foreign policy for a few years during George W. Bush’s first term. Biden himself was given a large mandate by Obama during the government’s response to the Great Recession, administering hundreds of billions of dollars in federal stimulus spending.

Harris got no such assignments, despite Biden suggesting that he wanted his second-in-command to be a governing “partner” during the 2020 campaign season. Questions about this have dogged Harris. Just nine months into Biden’s term, after waves of negative media coverage, public absence, staff departures, and rhetorical missteps (which have now become a genre of meme), the White House issued a statement assuring the public that the president did rely on Harris.

By that point, the idea that Harris served a superfluous role was already baking into public and media perception. Instead of working on issues like criminal-justice reform and policing — her areas of expertise — she took on voting rights, an issue that was doomed to fail in an evenly divided Senate. Her portfolio was then filled with another cursed assignment: dealing with the root causes of migration from Latin America. Mainstream press coverage of that task, and Republican framing of it online and in right-wing media, made it seem like her job would be dealing with immigration and the southern border, however. That fog made her an easier target for Republicans.

Still, something changed in 2022: When the Supreme Court overturned Roe v. Wade that summer and eliminated the constitutional right to an abortion, Harris suddenly had a clear lane in which to operate, and she has taken it: being the Biden administration’s point person on conservative threats to reproductive rights.

Post-Dobbs and since the generally successful midterms that followed later that same year, Harris’s official role has shifted. She’s been on more foreign visits and to gatherings of NATO and allied leaders, headlined a national college tour, and embarked on two other nationwide tours: one this winter dedicated to raising awareness of threats to reproductive freedom (it kicked off on the 51st anniversary of Roe v. Wade) and another this spring focused on “economic opportunity.”

The tours, though events run out of the White House, served a campaign function as well. The stops were concentrated in swing states, and meant to reach a swath of core Democratic constituencies that Harris may be better positioned to speak to like young voters and college students, women, Black and Latino Americans, and working-class communities. Unlike Biden, who has been struggling with voters from all of these backgrounds, Harris is a natural communicator in these settings.

The change in these official duties has also resulted in a shift in her campaign role, especially as the primary season wrapped up this spring and the general election began. She made history, the White House said, when she visited and toured an abortion clinic in Minneapolis in March, and has since delivered campaign speeches in states that have taken measures to restrict abortion access, like Florida and Arizona, both when the state’s top court allowed a century-old abortion ban go into effect and again on the second anniversary of Dobbs.

She’s filling the void that Biden has created intentionally (because of his age) or not (because he is also president, governing the country). Thursday night’s interviews, and whatever appearances she will have to make to defend Biden, show us what is likely to come: an expanded role for the veep in this term and a theoretical next.

Biden will need it and Democrats should want it, in the event that Harris has to step up to win the election, govern the nation, or just be a solid backup — precisely as the vice presidency is supposed to work.