Hillary Clinton's campaign was worried about the "hard balance" she would need to strike as the presidential candidate prepared to oppose a Pacific trade pact championed by President Barack Obama that she once supported, according to emails published on Tuesday by WikiLeaks.

WikiLeaks released its latest batch of apparently hacked personal emails of Clinton campaign chair John Podesta with exactly four weeks left in the 2016 presidential campaign before the Nov. 8 election.

White House hopefuls have made trade a key theme of their campaigns, with the 12-nation Trans-Pacific Partnership (TPP), a prime target for criticism by both Democrat Clinton and Republican opponent Donald Trump.