National Security Advisor Jake Sullivan highlights Ukraine's need for ammunition against Russia.
The purchase contract aims to replenish Ukraine's weapon stock.
Concerns arise about the sustainability of future funding for Ukraine's military support.
GOP reluctance in the House inhibits long-term military aid for Ukraine.
Weapons support includes crucial items like 155mm shells and HIMARS rockets.
Previous accounting errors did not affect the quantity of weapons sent to Ukraine.
The HIMARS system proves effective against Russian forces in the Ukrainian conflict.