I think so, could be power-problems, but think of the whatever could happen with timetravel... If they send an entiry army, there is a lot of publicity, then, people realise skynet is the problem, never create it, so the terminators wheren't send, building skynet etc. etc. etc. (timeloop) I think it is better to send the t-x to the beginning of the war, ensuring the victory with the knowlegde of the future (where-abouts and such).