Kamala Harris says she’s ‘not Joe Biden’ but reluctant to explain how

But when pressed for specifics on how she would be different as president, Harris has refrained from detailing a contrast with Biden, as she navigates the complexity of running as a change candidate—with the slogan “A New Way Forward"—while also serving as vice president.

Harris prioritized loyalty to Biden over the last 3½ years—at times over her own political capital. As a candidate to succeed him, she is wary of being critical of the president and an administration she is still a part of, Harris allies say. She has, however, embraced a handful of economic and border policy proposals her advisers have crafted with an eye toward making a break with Biden clearer to change-hungry voters.

Asked on ABC’s “The View" Tuesday if she would have done anything differently than Biden over the last four years, Harris at first responded: “There is not a thing that comes to mind," before saying at the end of the interview that she would appoint a Republican to her cabinet.

Later that day, on CBS’s “The Late Show with Stephen Colbert," Harris instead articulated the differences between her proposals and those of Donald Trump, the GOP’s nominee, when asked a similar question. “It’s important to say with 28 days to go, I’m not Donald Trump," she said.

Trump played the “not a thing" clip from Harris at his rally in Scranton, Pa., on Wednesday. “Can you believe our country is being run by these people?" Trump said, before criticizing the Biden administration on the chaotic withdrawal of U.S. troops from Afghanistan, the border and inflation.

Trump and his allies are trying to erode what has been a Harris advantage: She is more popular than Biden. Her favorability and unfavorability ratings in national surveys are nearly identical, poll averages show, while Trump and Biden are both several points underwater.

For all the GOP’s efforts to lump Harris and Biden together, a recent poll by the New York Times/Siena College gave Harris a narrow edge over Trump, 46% to 44%, on which candidate represented change. Harris holds a slight head-to-head lead in most national polls, and swing-state surveys have been essentially tied.

Still, Harris’s responses this week surprised some Democrats who believe her campaign has so far offered nuanced, wonky differences from Biden that might be unclear to voters who aren’t reading policy papers.

“They were a missed opportunity to do something voters will reward," said Evan Roth Smith, a Democratic pollster for Blueprint, which found that messages that showed a clear break from Biden on specific issues performed the best with voters overall and with independent voters. Those that characterized a Harris administration as building on the Biden administration’s work, meanwhile, performed the worst.

“She doesn’t need to stab the president in the back," he said. “Just pick a specific issue that is of high importance to voters and draw a really clear distinction."

Harris’s advisers have in recent weeks stressed incremental policy changes to position her as more business-friendly and tougher on the border than Biden, who gets poor marks from voters on the economy and immigration.

Harris proposed a less drastic increase in the top capital-gains tax rate, breaking with a plan Biden outlined in his budget blueprint earlier this year. Her overall economic message has also shifted away from Biden’s emphasis on jobs and workers to one on prices and consumers.

The vice president said during a visit to the border that she would go a step further than Biden’s recent border crackdown and make it harder to lift restrictions blocking migrants from asking for asylum if they crossed illegally.

But asked directly about Biden and her vision, Harris in her media blitz this week didn’t highlight those policy differences. Instead she spoke broadly about her economic vision, “the significance of the next generation of leadership" and how her own personal experience would influence her presidency.

Policies aside, Harris, 59, a daughter of immigrants who would be the first female president, already presents a contrast with Biden, the oldest sitting president. Some of her allies argue that putting too much daylight between her and the incumbent risks alienating some Democratic voters who still have affection for him. It could also directly contradict the president’s recent comments that he and Harris are “singing from the same song sheet."

But several Democrats also noted Harris has room to distance herself—at least in rhetoric—on another vulnerability for both of them: the intensifying conflict in the Middle East.

Israel’s airstrikes and its widening ground operation in southern Lebanon have displaced hundreds of thousands of Lebanese, while the Biden administration has been frustrated with being caught off guard by Israel’s military actions in Gaza and Lebanon.

Even if she doesn’t offer a clear policy shift, they said that Harris can be much more critical of Israeli Prime Minister Benjamin Netanyahu. The vice president came close in a recent interview with CBS’s “60 Minutes," declining to describe Netanyahu as “a close ally."

“I’ve been surprised by just how allergic to even inching in the direction of antiwar voters Vice President Harris has been," said Abbas Alawieh, a co-founder of the Uncommitted movement.

Alawieh noted he has spoken with many Democratic officials as part of the Uncommitted movement’s efforts to push for a policy shift in the Middle East, and that they all want Harris to be more critical of Netanyahu.

“I don’t know that being more critical of Netanyahu would cost a single Democratic vote. It might gain us some votes," he said. “I think that would mobilize a lot of Democratic voters, actually."

Natalie Andrews and Sabrina Siddiqui contributed to this article.

Write to Tarini Parti at tarini.parti@wsj.com