Trump is storing the 2nd dose so we know everyone gets their 2nd dose.
Scott Gottlieb was asked that on Face the Nation yesterday. He said that the labs are producing additional doses of vaccine all the time and there will not be any reason why the supply for the second does wouldn't be available. There are two more companies producing vaccines - AstraZeneca is expected to get FDA approval any day now and Johnson & Johnson is also expected to have a vaccine which will require only one-shot and it doesn't have to be refrigerated at other than normal temperatures.