President Joe Biden's endorsement of Vice President Kamala Harris as the Democratic nominee for president has set the stage for a much tighter and uncertain race in November, according to some experts

Biden stepped down from the race Sunday as top Democrats had been urging him to drop out following a disastrous debate performance and as Republican nominee Donald Trump was leading in the polls.

The Democrats had been headed for a "landslide defeat" in November, but now, they stand a chance, said Ian Bremmer, President and Founder of Eurasia Group.

"They've turned [this race] around, and President Biden has given the Democrats a fighting chance," he told CNBC's "Squawk Box Asia" on Monday.

Harris now finds herself on a glidepath to the Democratic nomination, though she will still need to win a majority of delegates ahead of the Democratic National Convention in Chicago in August. 

While some other contenders might throw their hat into the race, "it is very clear that Kamala Harris is the prohibitive favorite to become the nominee," Bremmer said. 

If Harris wins the nomination, she would offer the Democrats a "total reset," Steven Okun, founder and CEO of APAC Advisors, told CNBC's "Squawk Box Asia."

"If the Democrats can be unified, come out of this convention, speaking with one voice, energized, excited, then they have a good chance to win in November," he said.

Allan Lichtman, a presidential historian who has correctly predicted the winner of every presidential election since 1984, told CNBC's "Capital Connection that Harris would be in a "strong position to win the upcoming election" in a match-up with Trump.

He will wait until the Democratic convention to make his official prediction.

Harris said in a post on social media platform X that she was looking to work to "earn and win" the nomination while uniting Democrats.

According to experts that spoke to CNBC, Harris comes with a number of advantages in comparison to her former running mate. 

While Republicans have been gaining ground on the economy, inflation, and immigration fronts, abortion is a salient issue where she will have an edge, Okun said. Harris has been outspoken on reproductive issues as the first women Vice President.

"The fact is that Biden and Trump are too old to be running and serving for another four years, and this is now the top vulnerability for Trump," said Eurasia's Bremmer.  

A recent poll showed that some 85% of the population believed Biden was too old to serve another four years. The same poll found that 60% of Americans thought Trump was too old.

"You see a lot of enthusiasm for Harris, a younger, more vibrant, more energetic former prosecutor that could certainly perform extremely well on the debate stage," Bremmer added. 

Bremmer pointed out that Harris also has some weaknesses. She "isn't super likable as a retail politician ... That's been a vulnerability for her."  There are also some risks associated with running as a woman — a daughter of an Indian mother and Jamaican father — in today's America, he added.

On the other hand, she may be better-positioned than Biden to drive out certain key demographics, including "women, young people and black voters, Charles Myers, Signum Global policy Founder and CEO, told CNBC's "Squawk Box Asia."

"It's a whole new race. There's a new candidate with an enormous amount of unity and enthusiasm behind her," he said.

Markets had increasingly been pricing in a Trump victory, whose presidency is expected to bring in tax cuts and a stronger tariff policy. 

However, according to Myers, the race has been thrown into "complete disarray" with Harris set to give Trump a "real run for his money."

"I'd be very wary and a bit cautious on assuming that Trump is just going to sail to victory," Myers said, adding that the names and asset classes associated with a Trump victory could be perceived as having short-term risk. 

Trump has said that Harris would be easier to defeat compared to Biden. 

By the Democratic Convention, Harris would have picked a running mate and likely wrapped up the nomination, at which point the momentum could see her pull ahead in the polls, Myers said. 

According to Okun, two likely frontrunners for Harris's running mate are Governor Josh Shapiro of Pennsylvania and Senator Mark Kelly of Arizona, as they come from key swing states and are seen as more moderate.

If the Democrats are unable to unify factions within the party such as moderates and progressives, they will lose to a Republican party that is completely unified around Trump, he added.

— CNBC's Sonia Heng contributed to this report.