I'm sitting here watching Terminator: The Sarah Connor Chronicles (TSCC for short). Thinking about it, I think they've made a storytelling mistake in altering the rules of time travel. I'm not just talking about the idea that Skynet sent back more Terminators, or that the Resistance managed to send back yet another subverted Terminator. No, it's bigger than that.
TTSC has a running subplot about the Resistance sending fighters back through time to establish covert cells in the present, with agents having been sent back at least as far as the 1960s. These agents managed to build a time machine in the 1970s, using period parts no less, hidden inside a bank vault.
So not only do both sides send new cyborgs back from the late 2020s, but there is aparently some kind of geurilla war going on. It is implied that two-way time travel is possible (since Sarah, John and Cameron travel from 1997 to 2007), but that the soldiers from the future can build future tech weapons and gadgets from spare parts.
Now, admittedly, the rules weren't consistent from movie to movie, and sending more machines back is a staple of the franchise. But within the story of each movie, time travel was a closed issue. It was a gimmick to get the story started, and everything else happened here-and-now. The logical problems of time travel were ideas to play with in between action sequences. The had no real bearing on how the story unfolded. This kept things neat, even if it did provide many moments of
fridge logic.
But that limit is off, now. Time travel is part of the main story, which lets in all the pitfalls to which time travel stories are heir. I probably don't need to detail how many fans thought that the Temporal Cold War story arc was the biggest problem with Star Trek: Enterprise. Keeping the internal logic of the story from collapsing in on itself is going to get harder as the story goes on, faster the more they include more instances of time travel.
Judging by the history of time travel stories so far, the chances aren't good. The TV shows that have included time travel as a major plot element thus far have succeeded only under one two conditions.
In the first kind, time travel was seriously restricted, either happening only once or twice, or having rules that limited its use to that which the writers could handle. The Babylon 5 stories dealing with time travel and Babylon 4 are excellet examples of this.
In the second kind, time travel is not taken terribly seriously. It's just a gimmick to get the characters into the story, and give them an out again. It's a kind of
reset button, allowing each story to be neatly compartmentalized in its own bubble of space and time.
TSCC looks like it isn't going the first route. And I'm not sure it can go the second route without losing something of the drama it hasn't already lost to that insipid high school drama subplot.
Personally, I blame the
Time War. Back in the old days, the Time Lords would never have allowed this kind of thing to happen.