While Biden fumbles at the podium, Kamala Harris is doing her best at playing presidential

• While Biden continuously fails to reassure voters of his fitness, Harris has been doing the opposite.
• On Thursday, Harris did her level best to shore up support at a rally in North Carolina.
• Harris may be one of the most likely replacements for Biden if he were to step aside.

While President Joe Biden tried to keep it together at his big boy press conference on Thursday , his vice president was at a rally in North Carolina putting up a much stronger show.

The pressure to perform well was high in Biden's live press appearance — his first unscripted dialogue since the disastrous CNN debate that had Democratic lawmakers and donors questioning his fitness to run for reelection.

And Biden did not provide much reassurance to his supporters. On Thursday, he fumbled — with gaffes like calling Vice President Kamala Harris "Vice President Trump," and mistakenly addressing Ukrainian President Volodymyr Zelenskyy as "President Putin."

In contrast, Harris was out on the campaign trail in North Carolina, delivering strong, articulate messages about the president's capabilities.

"If there is one single person who deserves credit, in the world, for strengthening NATO, making it stronger, making it more united and more effective, that is Joe Biden," she said.

"And having made it more effective, then together with our allies around the globe, we are standing up to the dictator Putin. All to ensure that America is strong and Americans are safe," she added with her voice raised, to loud applause and cheers.

Harris' performance, particularly in contrast with Biden's, did not go unnoticed.

Rep. Jared Huffman of California reposted Harris' North Carolina campaign speech on X on Thursday, writing : "VP Harris is on fire. She's vetted, tested, and has been Democrats' strongest messenger throughout this campaign.

He added: "Let me be very clear: if/when President Biden passes the torch, I'm all-in for Kamala Harris!"

Former CNN correspondent and political commentator Brian Stelter echoed Huffman's sentiments, saying on X: "Many powerful sound bites from VP Kamala Harris on the nightly newscasts right now."

Harris may be quietly gearing up for a 2024 run

Rumors have been brewing that Harris may be quietly preparing to take over the Democratic presidential ticket from Biden.

For one, her staff changed her schedule after the June CNN debate, having her appear alongside Biden for the Fourth of July fireworks and picnic at the White House, something she has not done before, The New York Times reported .

She had always traditionally celebrated the day at a local fire station.

And Al Sharpton, a civil rights leader who spoke to Harris on July 5, told The Times that people around Harris were gearing up for the possibility that they might have to make her the Democratic candidate.

"I think there are some that are independent of her that are getting ready," he told The Times.

And surveys have shown that Harris may be a viable Biden replacement.

A new Thursday poll , conducted jointly by ABC News, Washington Post, and Ipsos, showed that if Harris ran for the top job instead of Biden, she would have a two-percentage-point edge over former President Donald Trump.

Biden's campaign manager has also said that if Biden quits, most of his campaign's sizable war chest will go to Harris.

It's not just members of the Democratic Party. In a video posted on his Truth Social account on July 3, Trump, too, acknowledged the possibility of running against Harris rather than Biden.

"I got him out the race, and that means we have Kamala," Trump said in the clip.

In anticipation of a switch of candidates, Trump is already trialing some nasty nicknames for Harris, including "Laffin' Kamala Harris" and "Cackling Copilot Kamala Harris."

Harris has remained loyal — for now

Despite mounting pressures on Biden to step aside in favor of a younger and more viable candidate, Harris has stood resolutely behind the president.

And to be sure, while Harris is Biden's most likely replacement, other names have been floated, like Gov. Gavin Newsom of California, Gov. Gretchen Whitmer of Michigan, Sen. Amy Klobuchar of Minnesota, and more.

Newsom and Whitmer have both publicly affirmed their support for Biden, saying they would not challenge him in the race.

And Biden, too, is hanging in there despite at least 16 House Democrats and one Democratic senator calling on him to quit.

In a letter to House Democrats on Monday, he said: "I wouldn't be running again if I did not absolutely believe I was the best person to beat Donald Trump in 2024."

Representatives for Harris did not immediately respond to requests for comment from Business Insider sent outside regular business hours.