This makes for major cause-and-effect headaches. Doesn't messing with the past on this scale change the future in itself, especially considering the previously mentioned butterfly effect (meaning: any minor change will have major consequences)? And if the Terminators didn't find themselves blinked out of existence after sending the first machine back, why send a second one? Didn't Sarah obviously fail to avoid the war? And why does Sarah want to avoid that future even though it likely means that her son will cease to be? Alternatively, in the case that changing the past doesn't erase the future but results in the creation of an alternate timeline, why bother going after someone in the past who can't affect 'your' reality? Is your head hurting yet?

Apart from the special effects budget, I have to wonder why the improved, liquid metal Terminator model has not shown up yet. Is the future saving him as a last resort? And why wouldn't the last resort be sent back to an earlier point in time, as you don't have to be linear when time-traveling? It is somewhat worrying that all this shaky logic is at the core of the plot, but not being discussed. Maybe the show runners are just stalling to be able to come up with a coherent explanation. The only way to enjoy the series is to let go of all reasoning, just watch the action and not ponder any of it.

As it stands, Terminator: The Sarah Conner Chronicles serves as a run-of-the-mill action series with average writing that will need to find a way to stand out from the competition, aside from its affiliation with the Terminator franchise.