The problem for soon-to-be President Trump is that he has not nominated anyone for the FEMA position as of yet. There will certainly be an "acting administrator" whose name has not been announced yet, or known by me. People in acting positions make for poor surrogates for actual appointees when it comes to fixing blame. Without a permanent FEMA administrator in place the fingers will point directly back to Trump for failing to appoint someone in a timely manner.
As has been noted by the national news, there are only a few days of grace period, but as things start to happen, the aspect of being "responsible" will settle in on the new administration. There will be no one else to blame for things that go wrong. They will own the disaster response and if it goes poorly, they will be accountable for the negative results.
Brandon Hardenbrook shared the link above.