Dow, S&P 500 dip ahead of US presidential debate

The Dow edged lower in opening trading Tuesday as markets await the first US presidential debate amid partisan warring over a Supreme Court nomination and another federal stimulus package.

About 20 minutes into trading, the Dow Jones Industrial Average was down 0.3 percent at 27,503.73.

The broad-based S&P 500 shed 0.1 percent to 3,348.62, while the tech-rich Nasdaq Composite Index was flat at 11,121.36.

Tonight's debate in Ohio pits President Donald Trump against Democratic challenger Joe Biden and comes after US politics were rocked anew by revelations from a New York Times expose that said Trump paid no taxes for 10 of the last 15 years.

The political parties are already far apart on Trump's nomination of Amy Coney Barrett to the Supreme Court and over the $2.2 trillion stimulus proposal pushed by Democrats in Congress, a sum Republicans say is excessive.

Biden is ahead in national polls and in several crucial swing states, but a debate win by Trump could shake up that dynamic.

Markets are looking ahead to the release of consumer confidence data, which analysts expect will show a modest bounce from August.