Presidential hopefuls must walk a fine line to defeat U.S. President Donald Trump, presenting their own views while fending off his attacks, said former Secretary of State Hillary Clinton, who lost to Trump in a bitter 2016 race.

Speaking on Friday, the fourth anniversary of the day she declared her bid for president, Clinton said in a New York appearance she was "delighted" about the diverse Democratic field, with a record six women, vying to challenge Trump in the 2020 election.

Clinton, who is also a former U.S. senator and former first lady, lost to Trump in November 2016 in a stunning upset.