Former US Vice President Joe Biden speaks during a 2020 Democratic presidential debate in Houston, Texas, Sept. 12, 2019. Photo: Reuters / Mike Blake.

Former Vice President Joe Biden, the front-runner for the Democratic presidential nomination, said on Sunday the party may be forced to host a “virtual” nominating convention in August due to concerns about the coronavirus pandemic.

The Democratic Party already postponed its convention from July to August last week, citing worries over the outbreak that has prompted a majority of US states to order their residents to stay at home to contain the disease’s spread.

“We may have to do a virtual convention,” Biden said on ABC‘s “This Week” program. “I think we should be thinking about that right now … We may not be able to put 10, 20, 30,000 people in one place.”

Biden and rival Senator Bernie Sanders have been forced off the campaign trail, and more than a dozen states have postponed their primary elections. Wisconsin, however, plans to hold in-person voting on Tuesday despite calls for a delay.

After a series of victories in March, Biden has opened up a commanding lead in the number of delegates needed to secure the party’s nomination to take on Republican President Donald Trump in November’s general election.

Though Biden is not holding in-person campaign events, he said he would follow new federal guidelines calling for people to cover their faces in public. Trump announced the revised recommendation on Friday but said he personally did not plan on wearing a mask.

“Listen to the experts,” Biden said. “Do what they tell you. He may not like how he looks in a mask, but the truth of the matter is that — follow the science, that’s what they’re telling us.”

Biden again questioned Trump’s handling of the crisis.

“He’s moving too slow,” Biden said. “The virus is not his fault, but the response is his responsibility.”

Trump has faced criticism for initially downplaying the threat from the coronavirus. Several governors have clashed with his administration over a lack of medical supplies, including ventilators.

The president has defended his response to the outbreak and suggested some governors are exaggerating the number of ventilators they need.

Biden also said he had called Sanders as a courtesy to let him know he was starting to vet potential vice presidential candidates, even though the Democratic race is not over, to ensure Biden’s campaign has time to complete the necessary background checks.

“I was basically apologizing and making it clear that I wasn’t trying to be presumptuous, in any way push him,” Biden said. “And he said he appreciated that.”