Considering "can" versus "will be able to"...
Each of the actions occurs at a different moment in time:
- the next attack (in December)
- cut off the supply line (beginning of 2025)
Therefore at the time of the attack, and even after it, the supply line remains intact. The cutting will occur afterwards, at a later point in time. This fact about the timing is elucidated and confirmed by the proper sounding phrase "will be able to", which is a good choice.
"Can" is not wrong, per se. It's simplified. It sounds colloquial. When somebody is speaking quickly and conversationally, they often use the simple present tense in place of other tenses (both past and future).
Therefore it matters if this is formal written communication or casual conversation. That's a determining factor. I would suggest "will be able to" is the correct answer in most written formats while "can" is acceptable, especially in speech. Although, the more I think about it, the more I prefer "will be able to" for this particular case.