WILMINGTON, Del. — Joe Biden on Wednesday expressed reservations about whether a coronavirus vaccine approved by the Trump administration would be safe, raising doubts about the president’s ability to put the health of Americans before politics.

Biden said Americans should trust a coronavirus vaccine developed under the Trump administration only if the president gives “honest answers” to questions about its safety, effectiveness and equitable distribution. “I trust vaccines. I trust scientists. But I don’t trust Donald Trump,” Biden said. “And at this point, the American people can’t, either.”

Biden also raised the possibility of President Trump pressuring agency officials to sign off on a vaccine that scientists are not yet confident in, to gain an electoral advantage.

The comments, which echo suspicions Biden has expressed in recent weeks, highlight the extraordinary division between the two candidates. Biden’s remarks also show how the pandemic has become a focal point in the final weeks of the race.

Biden campaign advisers have long felt that the election will be a referendum on Trump and his handling of the pandemic, which has stoked widespread anger and received low marks in public polls. They continue to hold events and run advertisements focused on this theme.

Trump has pressed health officials to accelerate the vaccine timeline and deliver one by the end of the year. At a news conference Wednesday, the president said that the vaccine “could be announced in October” and that as soon as it is available it can be distributed “immediately” to the general public. “To the general public immediately — when we go, we go,” he said.

If a vaccine is swiftly approved, it could upend the campaign. However, experts have said it is unlikely that a vaccine could be approved and come into full circulation before the Nov. 3 election.

Centers for Disease Control and Prevention Director Robert Redfield told senators Wednesday that after a safe and effective vaccine becomes available, it probably will take six to nine months for enough Americans to get vaccinated to significantly affect the pandemic.

Redfield said he expected a vaccine to start being available in November or December, with the first people to receive it being those with health problems that make them most vulnerable to a severe case or death if they are infected.

Biden spoke here in his hometown after receiving a briefing from experts about developing and distributing a vaccine. Creating the drug is only “part of the battle,” said Biden, who likened effective distribution to a complex military operation.

The former vice president said that a vaccine should be free and that priority should go to those who need it most — and that includes Black and Brown communities.

Biden received his briefing virtually from experts who appeared on a large screen that was set up inside the downtown theater where he spoke. He sat at a desk and listened to his briefers, which included some boldface names from the Obama administration.

Among the participants were former surgeon general Vivek H. Murthy; Zeke Emanuel, chair of the Department of Medical Ethics and Health Policy at the University of Pennsylvania; former Chicago health commissioner Julie Morita; and former Food and Drug Administration commissioner Peggy Hamburg.

Biden cast doubt not only on Trump but also on those around him. Asked whether he trusted the CDC and FDA, Biden said he did not trust “people like the fellow that just took a leave of absence.” He appeared to be referring to Michael Caputo, assistant secretary for public affairs at the Department of Health and Human Services, who urged Trump’s supporters to prepare for an armed insurrection and accused scientists in his agency of “sedition.”

As Biden addressed reporters, he attacked Trump’s handling of the pandemic and comments in an ABC town hall defending his administration’s response, despite widely documented problems with it. Biden urged Americans to ask themselves how it made them feel to hear Trump say he would not have done things differently.

Biden said people should not expect results just because the president is talking up the possibility of a vaccine. “Scientific breakthroughs don’t care about calendars any more than the virus does,” he said. He warned that politics should have no place in the production of a vaccine.

The Democrat's position has become a point of contention in the campaign, with Trump accusing Biden and his running mate, Sen. Kamala D. Harris (D-Calif.), of spreading “anti-vaccine rhetoric.”

At a Wednesday news conference, Trump said Biden’s comments were “anti-vaccine” and “hurting the importance of what we’re doing.” He added, “I know that if they were in this position, they’d be saying how wonderful it is.”

Biden said he would have no problems endorsing a vaccine — provided it met certain criteria. If the administration greenlights a vaccine, Biden said, “who will validate it was driven by science? What groups of scientists?”

He added that Americans must be confident “distribution will be safe and cost-free,” with a plan that is “without a hint of favoritism.”

Polls show Biden leading Trump nationally and in key battleground states. But one area where Trump's standing has shown strength is his handling of the economy. Asked Wednesday why that is the case, Biden replied, “I’ve been out of office for four years,” arguing that voters do not have an immediate sense of the progress the Obama administration made.

Biden also lambasted Trump for not aggressively encouraging mask-wearing and alleging that waiters do not like to wear them. The Democrat defended his own calls for a national mask mandate, saying he would seek to implement one by working with governors but was not completely sure yet what legal authorities he would have to deploy such a rule. (He said his advisers think they can create a mandate.)

He also sought to rebut attacks Trump has lobbed at him for unrest across the country. “I’m not the president. He’s the president,” Biden said, arguing that his opponent should be held to account for the country's woes.

Amy Goldstein in Washington contributed to this report.