Welcome back to your weekly update on US politics, where North America bureau chief Jade Macmillan catches you up on the biggest developments in America as we hurtle towards election day in November.

American political parties sure know how to put on a good show.

Over four days in Chicago, the Democratic National Committee rolled out a slick, made-for-TV (and social media) production peppered with former presidents and surprise celebrity guests.

The convention had one main purpose: to turbocharge Kamala Harris's month-old bid for the White House, ahead of the final stretch of the election campaign.

Democrats inside the arena exuded optimism. 

They danced in the stands, chanted new campaign slogans with gusto, and waved around cardboard cut-outs of Harris's face.

And over and over, in our conversations with delegates, the same adjectives kept being offered up: excited, enthusiastic, motivated.

It's impossible to know how different the atmosphere would have been had Joe Biden still been the party's nominee.

But underneath the joy in the room, there appeared to be a sense of relief.

Democrats could start their long farewell to the president — acknowledging what they see as his sacrifice in dropping out — before quickly turning to a new candidate who wouldn't make them nervous as she walked out onto the stage.

Harris's rise to the top of the Democratic ticket has up-ended the race and given a previously anxious party a new-found sense of confidence.

But it wasn't all that long ago that momentum was widely assumed to be on the Republican side of politics.

At the GOP convention last month, up the road in Milwaukee, Donald Trump was hailed as a martyr after surviving an assassination attempt.

Delegates wore white patches over their ears in solidarity with the former president, and shouted "fight, fight, fight": the now infamous phrase he delivered in the minutes after he was shot.

Against an 81-year-old president under intense pressure over his age and mental acuity, Trump projected a message of strength.

Four weeks on, it's an entirely different contest.

But Democrats are being warned not to take anything for granted.

'We cannot be our own worst enemies'

Hillary Clinton is intimately aware of how it can all come crashing down.

In 2016, the-then Democratic nominee was leading against Trump in the polls.

Many assumed the former secretary of state and first lady would become America's first-ever female president — a milestone she has once again labelled the "highest, hardest glass ceiling".

But while Clinton won the popular vote, she lost the electoral college, paving the way for Trump to enter the White House.

"No matter what the polls say, we can't let up," Clinton told the convention, in a speech she later described as "cathartic".

"Don't get distracted or complacent."

Another former first lady, Michelle Obama, warned "a handful of votes in every precinct" could decide the election outcome.

"No matter how good we feel tonight, or tomorrow, or the next day, this is going to be an uphill battle," she told the crowd.

"So folks, we cannot be our own worst enemies … This election is going to be close."

It was a message reinforced by Harris herself, who suggested Democrats would need to come down to Earth fairly quickly.

"I know we're going to get this done. We're going to win!" she told an after-party inside the arena.

"But only if we understand you can party tonight and you need to work for the next 75 days or so."

Harris doesn't have time to mess around. Biden's last-minute withdrawal from the race has left her with a very limited window to sell herself to undecided voters.

It also leaves less time to rebound from any stumbles.

That risk has been minimised so far, with the vice-president mostly sticking to the script with pre-prepared speeches.

The party's post-convention high shows that strategy has worked up to this point.

But it can't be sustained indefinitely. Harris has flagged doing a major interview by the end of this month, and her high-stakes debate against Trump is just over two weeks away.

The RFK Jr wildcard

Harris could also be hampered by Robert F Kennedy (RFK) Jr's decision to suspend his independent presidential bid.

The nephew of former president John F Kennedy had benefited from a cohort of so-called "double haters": voters who were unhappy with both Trump and Biden.

But Harris's entrance to the race exacerbated flagging political and financial support for his campaign.

While a bus decked out in RFK signage was doing late-night laps of the Democratic convention venue as recently as Thursday night local time, by Friday he'd announced he was getting behind Trump instead — a decision he described as "heart wrenching".

"This decision is agonising for me because of the difficulties it causes my wife and my children and my friends," he said at a press conference.

"But I have the certainty that this is what I've meant to do."

RFK Jr's polling numbers had slipped into the single digits, but in an incredibly close race, any support he drew away from either major party candidate could have an impact.

Harris's campaign made an appeal to his backers, arguing that anyone who was "tired of Donald Trump" should swing behind the vice-president.

But Trump's campaign was quick to claim RFK Jr's withdrawal had given its side the upper hand, citing its own surveys to argue it would deliver more votes to the former president.

"This is good news for President Trump and his campaign — plain and simple," a memo read.

One to watch: The rising stars in the spotlight

Political conventions can be an opportunity for rising stars to get noticed on a very big stage.

Barack Obama's speech as a US senate candidate in 2004 earned him a reputation as a skilled orator and helped him on his path to the White House four years later.

This year, there was a new generation of up-and-comers whose speeches were being watched closely.

Wes Moore is Maryland's first black governor, and at 45 years old, he's the youngest Democrat currently leading a state.

Pennsylvania Governor Josh Shapiro was passed over as Harris's running mate, but is widely reported to hold higher ambitions.

Transportation Secretary and former presidential candidate Pete Buttigieg received a rapturous response from his many fans in the crowd.

And Michigan Governor Gretchen Whitmer caught attention by using her address to describe Harris as a "total badass".

If the vice-president loses this election, the party could look to one of its younger leaders to be the one accepting the nomination in four years' time.