But CNN medical analyst Dr. Jonathan Reiner said on Sunday that not only is the president’s timeline unrealistic, but that vaccinating much of America could take years.

“No vaccine will be distributed for Election Day,” he warned, saying that even if a safe and effective shot is approved by then, distributing it would come with supply chain and logistical challenges.

Then, the vaccine will be given in a specific priority order, with frontline health care workers and those in nursing homes getting it first.

“There’s an elaborate plan that’s going to go into this,” he said. “So it’s going to take a while to actually get the vaccine into people and vaccination will take probably two years.”

Trump last month said he was “optimistic” that a coronavirus vaccine could be ready by the election, but has also suggested the end of the year as a potential target date.

The CDC has also urged states to be prepared to distribute a possible vaccine by the end of October.

Moncef Slaoui, chief adviser to the administration’s vaccine effort, called that timeline “extremely unlikely but not impossible” in an interview with NPR, but said it’s best to be prepared just in case.