When a card effect instructs you to perform an attack twice, it means: “After you perform this attack for the first time, perform another attack against the same target using this weapon.” When performing the second attack, the weapon and target are not declared again as they remain the same, and any cost for the attacks is not paid again.
Because these effects (just Cluster Missiles and TLT currently) now use the language of "After you perform this attack", does that introduce simultaneous timing with other "After you perform an attack" and "After defending" abilities?
Previously the assumption was that any of those abilities would be resolved prior to the second attack. If the timing is the same then not only does that allow the attacker (with initiative) to perform both attacks prior to the defender using "After defending" abilities, but it should allow them to perform the second attack prior to using other "After you perform an attack" abilities, without giving up the opportunity to use them (using them twice after the second attack).
The Vader (crew) FAQ entry suggests that additional attacks preclude using any more "After you perform an attack" abilities (i.e. if you want to use those abilities, it has to be before the second attack), but there's been cases in the past where an FAQ entry is a specific exception to the normal sequence of events. And to take that a step further, it could mean that a defender without initiative would only get to trigger "After defending" abilities once when attacked multiple times (and perhaps introducing a case where Dengar could deny "After you perform an attack" abilities all together).
Edited by FireSpy