Kaine and Pence clash in US vice presidential debate

US vice presidential hopefuls Tim Kaine and Mike Pence launched into their only debate of the campaign Wednesday, immediately clashing on the reputations, experiences and policies of their bosses chasing the White House.

Democrat Kaine and Republican Pence squared off to highlight their capabilities as the men who could be a heartbeat away from the US presidency.

But essentially they were on stage fighting a proxy war for their running mates five weeks before Election Day on November 8.

Their bickering was so intense that they frequently talked over each other.

Kaine tried to frighten voters away from Trump, while Pence, the Indiana governor, attempted to portray Clinton as untrustworthy for the White House and a failure as President Barack Obama's first-term secretary of state from 2009 to 2013.

Tim Kaine, a US senator from Virginia, promoted himself as a deeply experienced local, state and national politician who would be the "right hand person" for Clinton, whom he described as trustworthy and more than capable in the role of commander in chief.

He tried to make the vice presidential debate all about Donald Trump, calling the Republican presidential nominee a danger to US national security and someone who denigrates women and minorities and appears to pay little in federal taxes.

"The thought of Donald Trump as commander in chief scares us to death," Kaine said.

"I can't imagine how Governor Pence can defend the insult-driven, selfish, me-first style of Donald Trump," Kaine said, vocalising his primary strategy of forcing Pence to on to the back foot about the brash Republican billionaire at every turn.

An imperturbable Pence, the governor of Indiana and a Christian conservative, calmly shot back.

"You would know a lot about an insult-driven campaign," he said, highlighting Clinton's relentless criticism of Trump and how she painted half of her Republican rival's supporters as "deplorables."

"We see entire portions of the world, particularly the wider Middle East, spinning out of control. The situation we're watching hour by hour in Syria today is the result of the weak foreign policy that Hillary Clinton helped lead in this administration and create."

Kaine drew Pence's ire by hearkening back to a remark from former Republican President Ronald Reagan that some fool or maniac with a nuclear weapon could trigger a catastrophic event.

"And I think that's who Governor Pence's running mate is," Kaine said.

Pence shot back: "Senator, senator, that was even beneath you and Hillary Clinton and that's pretty low."

Kaine, 58, and Pence, 57, are about 10 years younger than the presidential nominees. They each are fathers of a son serving in the US military, and they are seen as more engaged with their faith than Clinton and Trump.

Kaine, in a line that was clearly rehearsed, repeatedly sought to persuade Pence to defend Trump's positions.

He reminded the millions watching on television that Trump was enmeshed in a public feud with a former beauty queen last week, and he pointed out that Trump had praised Russian President Vladimir Putin.

On Russia, Pence stressed that a Trump administration would want the US to "use military force to strike the targets of the Assad regime" if Russia continued its involvement in "this barbaric attack on Aleppo."

But the Republican clearly distanced himself from Trump's praise of Russian President Vladimir Putin, hailing the US system as "superior to the crony corrupt cabal system in Russia in every way."

Kaine hammered away though, insisting that "Donald Trump, again and again, has praised Vladimir Putin and it's clear that he has business dealings with Russian oligarchs."

"Trump has business dealings with Russia that he refuses to disclose," while "Hillary Clinton has gone toe to toe with Russia."

Pence assailed Clinton while pushing a larger theme of change — something many Americans say they want — including his call for "repealing Obamacare lock, stock, and barrel."

While Kaine accused Trump at length of mistaking "leadership for dictatorship" by praising Putin as a strong leader, he gave a much more abrupt answer when asked what went wrong with the failed US reset of relations with Russia under Obama and Clinton.

"What went wrong with the Russian reset? Vladimir Putin," said Kaine.

"Donald Trump always puts himself first," Kaine said, pointing out that when Trump began his presidential campaign last year he called "Mexicans rapists and criminals" and had also voiced the "outrageous lie" that Obama was not born in the United States.

Pence reacted by saying, "Senator, you whipped out that Mexican thing again."

But Kaine's overarching objective was to hammer home that Trump has refused to release his tax records, unlike all other presidential nominees in modern history.

The New York Times reported last weekend that Trump had taken a $916 million tax loss in 1995 and may have avoided paying federal taxes for 18 years because of it.

"Governor Pence had to give Donald Trump his tax returns to show he is qualified to be vice president. Donald Trump has to give his tax returns to show he is qualified to be president," Kaine said.

Pence, who has a low-key style compared to Trump's signature bombast, said Trump as a New York real estate developer had created thousands of jobs and had used US tax laws as they were designed to be used.

"Why won't he release his taxes?" Kaine fired back.

Crucial time for campaigns

The two candidates interrupted each other so much in a bid to score points that the debate moderator, CBS News' Elaine Quijano, intervened at one point.

"The people at home can't understand either one of you when you speak over each other," she said.

The debate came at a crucial time for both campaigns. Clinton is seeking to take advantage of the report last week on Trump's taxes to build on her lead in national opinion polls.

Trump needs to rebound from a rocky performance in his first debate with Clinton last week with their second encounter coming up on Sunday in St Louis.

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.

By the end of the debate both US presidential candidates tweeted their support for their respective running mates.

A second round of presidential debates is set for Sunday. The format will be a bit different, with candidates fielding questions put to them by people in the audience.