If Biden is elected president, warm letters or a noisy summit between Washington and Pyongyang are thought to be gone.

US President Donald Trump once said that if he wins the November 3 election, he will negotiate nuclear deals with North Korea "extremely quickly".

Late last year, the North Korean central news agency (KCNA) once called Biden, the candidate for the Democratic presidency, a "rabid dog to be eliminated" for "insulting the dignity of the highest leader of Korea".

KCNA's comments came after Biden's election campaign ran an advertisement showing Trump shaking hands with Kim at the 2018 US-North Korea summit and a message critical of the North Korean leader.

After Trump came to power, the US and North Korea experienced months of intimidation and insults on each other.

The two leaders then met twice more in Hanoi and the inter-Korean border, and exchanged letters that Trump praised as "good".

Contrary to Trump's way of acting, Biden said he would not continue his policy of promoting personal diplomacy with Kim, calling the meetings between the two leaders a "futile project" and should only proceed if they are.

However, an unnamed Biden adviser said the former US vice president would not "shut down" the diplomatic door with North Korea.

As a former "deputy general" under Barack Obama, some parts of Biden's policy are said to be similar to the former US president's "persistence pressure" strategy, which means seeking to isolate North Korea.

"Many of Biden's campaign advisers have been in the persistent strategic group. They support a concerted effort with allies and take orthodox approaches to diplomacy, including relations with North Korea."

"Under Biden, North Korea will not have to face the same unforeseen military action concerns as Trump's style, but is likely to be put under more pressure," Chang said.

Although Biden pledged to work more closely with allies, his efforts could be stymied, as South Korean President Moon Jae-in pursues a view of more cooperation with North Korea, easing orders.

"So Biden's approach could create a conflict between Washington and Seoul," said James Kim, an expert at South Korea's Asan Institute for Policy Research.

North Korea has also made significant progress in upgrading its military capabilities since Biden was vice president of the United States, such as successfully testing the country's largest nuclear bomb, or developing names.

According to Evans Revere, a former US negotiator who worked with North Korea, the US arms control community is likely to have a strong voice within the Biden administration, convincing that it is time to accept.

That approach, however, helps North Korea achieve its long-pursued goal of consolidating nuclear capabilities, while Biden is almost certain to be tougher if elected president, leading to the risk of impulse.

"If Biden wins in November, North Korea is likely to take a serious step by the end of the year, like conducting a nuclear test or an intercontinental ballistic missile (ICBM), to warn the authorities.

Jung Pak, former CIA analyst and unofficial adviser to Biden's campaign, says any North Korean provocation could be a major boost.

"A nuclear test or ICBM by Pyongyang will provide an opportunity for the new administration to highlight the threat posed by North Korea, while also trying to build a consensus or agreement with allies on a legitimate policy.

"It's an approach that doesn't waste good opportunities from a crisis," she added.