It is a textbook game theory example.Depends on the base.
Right now though a big established base is a well known target.
If a potential adversary wanted to pull a Pearl harbor 2.0 lobbing ballistic missiles at a large established US Airbase within a few thousand miles would be a fair start and effective way to knock the US back for weeks if not months of operational capabilities if partnered with air and sea denial.
Although the US employs some very good air defence missile systems not enough.
The aim of smaller bases is to establish distributed operations.
An Enemy only has so many long range precision guided munitions to spare at a time so if made to choose between three bases one large and two smaller they will assume the larger one is more capable and more of a threat.
The smaller bases though can respond and assist the larger one in defence or repair. They can also shelter addiction assets.
Before Pearl harbor one of the good management choices made by commanders was just that. To move additional aircraft from the main base field to secondary bases around the island. When the attack happened the Japanese focused on the main base. The secondary bases managed to come in and out up a fight.
Simple calculation, the art is to estimate the unknown parameters.