Senator Kamala Harris branded the response to the COVID-19 pandemic under Donald Trump as the "greatest failure" of any US administration, as the debate between her and Vice President Mike Pence opened on Wednesday.
But Pence fired back by accusing Harris of undermining public confidence in a future coronavirus vaccine through her attacks on Trump's credibility.
"The American people have witnessed what is the greatest failure of any presidential administration in the history of our country," Harris, running mate to Democratic presidential candidate Joe Biden, said.
The US death toll from the pandemic has exceeded 210,000, with over 7.5 million people infected, the highest reported totals in the world.
Pence slammed Harris for her statements questioning whether a vaccine released under Trump could be trusted due to the intense pressure on the president to tame the pandemic.
"The fact that you continue to undermine public confidence in a vaccine, if the vaccine emerges during the Trump administration, I think is unconscionable," Pence said.