Donald Trump's fluctuating relationship with North Korean leader Kim Jong Un has gone from fire and fury to love letters, but Pyongyang's view of his rival is uncompromising: Joe Biden is a "rabid dog" who "must be beaten to death".
Despite stalemated talks, Trump -- who touts his personal relationship with Kim -- has vowed to make deals with North Korea "very quickly" if he wins a second term on November 3.
But if the Democratic former vice president is elected, he will take a starkly different approach, analysts and officials say.
Pyongyang despises Biden for his role in the Obama administration, which adopted a policy of "strategic patience", refusing to engage with North Korea unless it offered concessions first, or until the regime collapsed from within.
North Korea's official news agency excoriated him in its most recent references.
"Rabid dogs like Biden can hurt lots of people if they are allowed to run about," KCNA said last year, adding: "They must be beaten to death with a stick."
It also adapted one of Trump's preferred insults for his rival, "Sleepy Joe".
Biden accuses Trump of "emboldening" the North Korean leader and has said he would not meet with Kim without preconditions.
"There will be no love letters in a Biden administration," he declared in a reference to the Trump-Kim diplomatic bromance.
In the final presidential debate on Thursday, Biden denounced Trump for befriending Kim, calling the North Korean leader a "thug" and likening him to Adolf Hitler.
"He's talked about his good buddy, who's a thug," Biden said of Kim. "That's like saying we had a good relationship with Hitler before he invaded Europe -- the rest of Europe."
But Biden also indicated he was willing to meet with Kim, saying his condition would be that Pyongyang works to make the Korean peninsula "a nuclear-free zone".
- Talks deadlock -
Pyongyang would be hoping for a second Trump term, said Andrei Lankov, professor at Kookmin University in Seoul.
"Under Joe Biden, it will be a period of stalemate," Lankov told AFP.
"If Donald Trump is re-elected, they will behave themselves for a while in the hope that they can squeeze some serious concessions from him."
A fiery war of words between Kim and Trump raised tensions and fears of conflict in 2017.
But a rapid diplomatic rapprochement ensued, with Trump becoming the first sitting US president to meet with a North Korean leader at a landmark Singapore summit in June 2018.
The two leaders met twice more, with Trump repeatedly proclaiming their friendship, although nuclear negotiations remain deadlocked.
And Pyongyang has continued to develop and advance its arsenal, displaying an array of new weapons -- including a huge new intercontinental ballistic missile -- at a military parade this month marking the 75th anniversary of its ruling party.
Chung Min Lee, a senior fellow at the Carnegie Endowment for International Peace, credited Trump for his effort to meet Kim but added: "The problem is what did he do with it."
The US president's motivations were wrong, he told a video conference.
"Trump was fixated with the idea that Kim Jong Un was going to somehow bolster his image back at home as the US president who brought peace to the Korean people."
- Testing time? -
Biden has dismissed Trump's "photo-ops" with Kim as a "vanity project", telling the New York Times he would only meet with the North Korean leader with "an actual strategy that moves the ball forward on denuclearisation".
A Biden presidency would signal a return to more normal diplomatic processes, said Lee Soo-hyuck, South Korea's ambassador to the US, with painstaking negotiations carried out at lower levels rather than top leaders trying to strike an all-encompassing deal in a few hours of talks.
Biden's experienced foreign policy and security advisers held senior positions in the Obama administration, he told lawmakers.
"Rather than a top-down approach, I expect to see policies being reviewed and proposed at the working-level that are approved by the president."
Pyongyang will closely follow the election, analysts say, contemplating the best moment to test its latest missile.
If Biden takes over the White House, the beginning of 2021 will be "a sensible time", said Ankit Panda of the Carnegie Endowment.
The launch would act as a reminder that going back to "the old Obama policy" will only mean "our capabilities will continue to expand", he added.
Trump's re-election may delay an ICBM test, analysts said, but did not rule out the prospect completely.
"They will have everything ready for testing," Lankov said.
"And if they don't get the deal they hope for, they will do a lot of testing."