Donald Trump and his running mate JD Vance have endured a rotten week on the campaign trail, overtaken in the polls by the Kamala Harris campaign and overshadowed on the stump by the arrival of her folksy running mate Tim “Coach/Cool Dad” Walz.

But at least the GOP’s gloomy twosome hasn’t endured the fate of Robert Kennedy Jnr, who has been transformed from the third party candidate with the presidency in his gift to a punchline, the crazy guy who dumped a dead bear in New York’s Central Park.

A dead bear. In the heart of Manhattan. Discovered (and later abandoned) by a Presidential candidate, the son of the late liberal hero Robert Kennedy no less, while he was on a falconry trip a decade ago. These are disturbingly surreal times in American public life. But even so, Kennedy's efforts this week to pass off a, frankly, insane anecdote as somehow normal really does take the family-sized Kit-Kat.

“So I pulled over and I picked up the bear and put him in the back of my van because I was gonna skin the bear. It was in very good condition and I was gonna put the meat in my refrigerator,” he explained in a video filmed with the once popular comedian, Rossanne Barr, who herself has made the journey from the American mainstream to the fringes where conspiracy theorists reside. “But I then had to go to the airport and the bear was in my car, and I didn’t want to leave the bear in the car because that would have been bad.”

The punchline was that Kennedy decided to stage an “accident” in which a bear was mowed down by a bike - he happened to have a bike in the back of his van. “I wasn’t drinking at the time but I was with people who were and they thought it would be very amusing for anyone who found it.”

So far, so bizarre. And at this stage in the proceedings it is worth asking why any of this matters?

The answer lies in the recent history of American presidential politics, where third party candidates have played a decisive role in the outcome of elections. In 1992, the Texas-based billionaire Ross Perot won 19.7% of the popular vote, not enough to win the election - or even a single vote in the electoral college - but more than enough to deny President George HW Bush a second term. Bill Clinton took advantage of Perot’s presence and became president with the support of just 43% of voters. Eight years later, the outcome of a fraught election came down to Florida, where George W Bush “won” (thanks to an outrageously partisan intervention from the Republican majority justices on the Supreme) the state’s 25 electoral college delegates by a 245-vote majority. The outcome, and perhaps the history of the Middle East, would have been different had not the Green Party candidate Ralph Nader won 97,421 votes, votes that almost certainly would have swung heavily towards Gore if Nader’s name hadn’t been on the ballot.

READ MORE: Robert F Kennedy Jr.: The independent challenging Joe Biden and Donald Trump

In 2016, Donald Trump lost the popular vote but won the presidency with narrow victories over Hillary Clinton in six swing states thanks to the presence of Green candidate Jill Stein, who’s vote share in four of those six states exceeded Trump’s margin of victory.

This year, the Trump campaign had hoped Kennedy, the misbegotten son of RFK, who was assassinated in Los Angeles whilst campaigning to win the Democratic Party nomination in 1968, would fulfill the Nader/Stein role, attracting support from Democrats who had become disillusioned with President Joe Biden.

As with all things Trump, his strategy was about as subtle as his combover. But for anyone unable to join the dots, the former President helped steer the pencil, praising Kennedy’s decision to enter the race last April, and describing him as a “very smart guy. “And his heart is in the right place and he’s doing really well! I saw a poll, he’s at 22 percent. That's pretty good.”

Lest there be any remaining doubt, a long-time Trump donor, billionaire Timothy Mellon, floated the Kennedy effort with a $20m gift, topped up with another $5m this spring. That money, along with a contribution from the candidate's wealthy running mate Nicole Shanahan, was used to build out a campaign structure and grassroots organisation, and pay for an advert during this year’s Super Bowl estimated to have cost $7m. It was at times a shambolic operation, as even the best-financed third party campaigns have been through the years, but it was enough to make Kennedy a formidable presence in the race. By the time the first Presidential debate between Trump and Biden came around at the end of June, Kennedy, whose ratings had been hovering around the 12-15% mark, came within one good poll result of taking the stage alongside the two principal candidates.

Naturally disappointed, he accused the Republican and Democratic parties of colluding to keep him out of the debate. “Americans feel like the system is rigged,” he said. “This is exactly the kind of merger of state and corporate power that I’m running to oppose.”

If Kennedy thought he would be the beneficiary of a popular uprising against such establishment collusion, even if it only existed in his fevered dreams, he was sadly mistaken. In the weeks since that debate, his popularity has fallen while the public’s understanding of his fringe political views and, ahem, checkered personal history has grown. Even Trump has joined the pile-on, no doubt fuelled by polling which suggested that Kennedy, whose anti-vaccine views and conspiracy-minded musing resonate with the nuttier elements of the Trump base, might take more votes from the Republican than he would from the Democrats. “He’s a fake, a radical left liberal put in place to help them,’’ the former President suggested. “He is not a Republican so don’t think you’re going to vote for him and feel good.”

In the most recent polls, all of which were sampled before Kennedy fessed up to his dead bear escapades in Central Park, his support had fallen to 5% or less. Expect it to fall even further with the addition of Walz to the Democratic ticket, and the infusion of energy that has brought this week. The Harris campaign will receive a further boost, and Kennedy another punch in the guts, when the party convention comes around at the end of the month.

The disillusioned Democrats who had intended to support Kennedy are returning home to Team Kamala. Most observers expect his 5% share to shrink further. How much further?

“The more we learn about RFK Jr., the more evidence we find of his bizarre and abusive behaviour,” said Britt Jacovich, a director at the MoveOn Political Action group, which has thrown its weight behind the Harris campaign. “His behaviour with dead animals is disgusting and disqualifying and shows the American people who he truly is, and that’s why his entire campaign is in the gutter.”

Democratic strategist Liz Smith, who has been heading up the party’s social media campaign against Kennedy, was even more brutal. “He is a reckless, narcissistic, nepo baby who is seriously mentally unwell.”

Expect the pounding to continue all the way to election day, or until Kennedy’s is reduced to an insignificant rump and his hopes of influencing the November outcome as lifeless as the bear he dumped in Central Park.