Hillary Clinton and Donald Trump's running mates snatched the spotlight for the White House race on Wednesday, preparing to face off in their only debate of the campaign with the US elections just five weeks away.
Polls show Democrat Clinton gaining in the wake of a punishing week for her Republican rival Trump, who was hammered by controversies over his taxes, his charitable foundation and treatment of women.
The candidates' understudies — Democrat Tim Kaine and Republican Mike Pence — will take centre stage on Wednesday when they do battle before a national television audience that likely will be the largest to date in their careers.
For many Americans, it will be their first prolonged exposure to the men who would be next in line for the presidency if their side wins on 8 November.
Kaine, 58, is an affable senator from Virginia whose liberalism stems in part from his Catholic faith and experiences as a volunteer working in poor communities in Central America.
Pence, 57, is the Christian conservative governor of Indiana, as modest and polite in style as Trump is brash and insulting.
Both will want to convince undecided voters that their bosses are worthy of the Oval Office.
Pence's job will be to reassure Republicans at a time when Trump is mired in difficulties, many of his own making.
Pence will aim to be a "calming influence" on conservatives nervous about Trump, according to Joel Goldstein of Saint Louis University School of Law, a leading authority on the vice presidency.
"His challenge is to steady the ship, convince the American people that there is some adult supervision, some adult presence there, and to appeal to conventional Republicans," Goldstein told AFP.
Weighing heavily against the New York billionaire are a mediocre performance in his first debate with Clinton, followed by revelations of a $916 million loss in 1995 that may have meant he paid no taxes for several years, and criticism of his demeaning treatment of a former Miss Universe, Alicia Machado.
His campaign manager Kellyanne Conway promised a "fiery" Kaine-Pence debate.
"I think you'll see in Mike Pence somebody who is able to defend Donald Trump the running mate, but at the same time take the case right to Hillary Clinton," she said on CBS.
Pence, who spent a dozen years in Congress, is known for his discipline. He has prepared intensively for the debate, unlike Trump, who did little to practice for his 26 September encounter with Clinton.
"We expect them to throw a lot of mud," said Clinton campaign manager Robbie Mook, ahead of the debate in Farmville, Virginia.
"It's going to be very interesting to see how Mike Pence responds to questions about Trump's behaviour in the last week," he added, also speaking on "CBS This Morning."
Defending Trump has become second nature for Pence: he's had to put out fires on multiple occasions over the past months.
When Trump became embroiled in a bitter feud with the family of a Muslim-American army captain killed in Iraq, it was Pence who put out a statement hailing Humayun Khan as an "American hero."
Besides reassuring voters turned off by Trump's volcanic temper, Pence must attack Clinton while pushing a larger theme of change — something many Americans say they want — and laying out the Republican agenda.
Trump himself framed the showdown in similar terms at a rally in Prescott Valley, Arizona hours before the event.
"The debate will be a contrast between our campaign of big ideas and bold solutions for tomorrow, versus the small and petty Clinton campaign that is totally stuck in the past," Trump said.
But Trump has also warned that he will be "live tweeting the VP debate," potentially overshadowing his running mate during his moment in the sun.
Kaine, who served as Virginia's governor from 2006 to 2010, appears to have the easier task.
Since the first presidential debate, support for Clinton has risen to 44.3 percent against 40.6 percent for Trump, according to an average of recent national polls compiled by RealClearPolitics.
Kaine's role so far has been to attack Trump, and he will no doubt seek to force Pence into owning the controversial rhetoric of his running mate.
But Kaine too will likely be forced into defending Clinton, for using a private email server as secretary of state, as well as in other controversies that have undercut her trustworthiness among voters.
While the two men are seen as disciplined and far less blemished than Clinton and Trump, vice presidential clashes can be unpredictable, even though they rarely move the needle.
"Vice presidential debates often can be freewheeling, with so much ground to cover," Goldstein said.
Americans will have a second round of presidential debates on Sunday to look forward to. The format will be a bit different, with candidates fielding questions put to them by people in the audience.