Answer
$116,280$ different leadership structures.
Work Step by Step
The order in which the members are selected matters and no member can be selected twice.
Permutation of 20 distinct members taken 4 at a time:
$_{20}P_{4}=\frac{20!}{(20-4)!}=\frac{20!}{16!}$
But, $20!=20\times19\times18\times17\times(16\times15\times14\times ... \times3\times2\times1)=20\times19\times18\times17\times16!$
$_{20}P_{4}=\frac{20\times19\times18\times17\times16!}{16!}=20\times19\times18\times17=116,280$
