Democratic presidential nominee Joe Biden promoted the medical importance of vaccines on Wednesday—specifically a future one for COVID-19—while reiterating his staunch mistrust of his political opponent.

“Let me be clear: I trust vaccines. I trust scientists. But I don’t trust Donald Trump,” Biden said in Wilmington, Delaware. The former vice president called for a “totally transparent” process in developing a vaccine against the coronavirus that is based on expert advice and data. Such an improvement “would offer a way back to normalcy,” he said. “But it’s not going to happen overnight.”

Asked by a reporter if he’d support the rollout of a vaccine developed under the Trump administration if scientists conclude it’s both “safe and effective,” Biden said: “Absolutely. Do it. Yes.” His response comes as some Democrats have been torn over how to strike the right tone on the issue, aware that they could be accused of politicizing science in an effort to criticize Trump, who has dangled the idea of possibly releasing a vaccine before Election Day.

“It won’t go away like a miracle,” Biden said, responding to Trump’s claim during an ABC News town hall the previous night that the virus would somehow dissipate on its own “with time,” to scant evidence.