That's a common risk management tactic. It's literally in the textbook. Likewise, the Vice President flies on his own plane, Air Force Two, and never Air Force One. When the President and Vice President have to be in the same place at the same time, someone else in the chain of succession has to be kept somewhere else; most dramatically, when the President addresses a joint session of Congress, as in the State of the Union address, one cabinet member is named the "designated successor", is not allowed to attend, and is provided Presidential-level Secret Service protection for the duration.
That's a common risk management tactic. It's literally in the textbook. Likewise, the Vice President flies on his own plane, Air Force Two, and never Air Force One. When the President and Vice President have to be in the same place at the same time, someone else in the chain of succession has to be kept somewhere else; most dramatically, when the President addresses a joint session of Congress, as in the State of the Union address, one cabinet member is named the "designated successor", is not allowed to attend, and is provided Presidential-level Secret Service protection for the duration.