Hillary Clinton and Donald Trump bickered and traded insults in a fiery US presidential debate Monday, as they aggressively pitched their case to tens of millions of American voters. With the White House rivals in a dead heat six weeks before election day, Clinton from the get-go painted her Republican rival as out of touch and having a tenuous relationship with the truth, willing to say "crazy things" to get elected. "You live in your own reality" said the 68-year old Democrat, who accused Trump of launching his political career on a "racist lie" -- the birther conspiracy theory that questioned President Barack Obama's citizenship. Trump, who faces tough questions about his suitability for the Oval Office, started out with a more restrained tone -- he even ditched his red power tie for a more statesmanlike blue. But he quickly went on the offensive, repeatedly interrupting Clinton with verbal jabs. The celebrity businessman branded Clinton a "typical politician. All talk, no action. Sounds good, doesn't work."

He now has a real shot at being sworn in as the 45th president of the United States on January 20.

Six weeks out from election day the polls have tightened to a virtual dead heat.

Trump's biggest handicap may be accusations that he has a weak grasp of policy -- which he sought to counter by accusing his rival of sowing chaos in the Middle East during her tenure as secretary of state.

"It's a total mess, under your direction, to a large extent," Trump said.

But he appeared on shaky ground as he defended his refusal to reveal his plan for defeating the Islamic State group.

"You're telling the enemy everything you want to do. No wonder you've been fighting ISIS your entire adult life," he said of the group that only came to prominence in the last decade.

Clinton -- perhaps the most qualified presidential candidate since George Bush senior or Dwight Eisenhower -- has a massive organizational advantage, a bigger campaign warchest, a lead in the popular vote and is in a notably stronger position state-by-state. But she remains deeply unpopular. In a country split 50/50 between Democrats and Republicans, only 40 percent of voters say they have a favorable view of her.

In the last two presidential elections, young, black, Hispanic and Asian-American voters turned out in record numbers for Obama.

Clinton's campaign has struggled so far to match that level of enthusiasm.

Only 47 percent of voters aged 18 to 34 say they will definitely vote this time round, that is down from 74 percent when Obama was first elected.