I don't really recall 1 being that for or against that sort of thing. You had China invading Alaska and America annexing Canada, ect.
You had America making FEV which was a response to China making use of biological weapons.
Overall, I think the game held a neutral stance on the whole thing. After all, the message isn't about whose fault it was that the bombs dropped, it was what happens if that sort of thing happened at all.
Fallout 1 still had a healthy dose of demonizing old America, most notably with the formation of the Brotherhood of Steel. They formed because some US Army regiment was disgusted to learn that America was experimenting with the FEV against Chinese prisoners of war. The very founding of the Brotherhood of Steel was due to the fact that old America was immoral enough to experiment with human captives to create mutant super-soldiers, as if they became just as bad as Josef Mengele.
And of course, the US annexing Canada was them not caring about the rights of other nations so long as they win the war, while China's invasion of Alaska was due to America's greed for oil and not wanting to share it. So again, it was all "AMERICA BAD" from there on in.
2 on the other hand, I can definitely see seeing what the Enclave are like. I think at that point, people like Chris Avellone started to insert their personal politics which probably colored the final product. As mentioned in a previous post, you have the Vice President character mentioning he's a Republican, and the Chosen One having the option to say he's part of the problem. It's meant to be a joke, I'm sure, but considering the state of video games as they are now, hindsight is 20/20.
The Vice President is explicitly a gag on Dan Quayle. All of his quotes came from Quayle (or were attributed to him; I think some of them are apocryphal). Bear in mind the man had been out of office 6 years by the time Fallout 2 hit the shelves. It's the sort of trite, unimaginative, anti-Republican ribbing you saw everywhere in media back then, which was admittedly irritating but orders of magnitude less vicious than things are today.
In Fallout 2, not only did they turn the remnant of the Cold War American government into a shallow facsimile of the Nazis, they outright linked right-wingers in the NCR with the Enclave villains, showing how the authors of that game detested right-wing politics:
"Shaken by the assassination of Vice-President Carlson, right-wing elements seize control of the Congress and set the New California Republic on a path to military rule. Eventually the survivors of the Enclave found a new home in the ranks of the NCR."
So basically, not only are the American patriots in the Enclave the bad guys, not only can you not join them or talk them down like Fallout 1 did with the Master, but the right-wingers in the NCR are also evil, and when you give the latter their chance to seize power, the former joins them and takes over the NCR government.
You can't get any more partisan than that.
New Vegas I feel did try and bring everything back to a more neutral stance which I appreciate, but good luck seeing something like that again anytime soon.
Fallout 3 and New Vegas actually shifted more to the right. Fallout 3 had the good guys be a military force of altruistic Brotherhood heretics based in the Pentagon being led in battle by a robot who talks about how bad Communism is, with symbols of American patriotism like the Lincoln Memorial and the Declaration of Independence being available for the player to take or restore.
Fallout New Vegas shifted even farther to the right, portraying an unapologetic capitalist as the most level-headed of all the faction leaders while the liberal democracy is an inefficient mess when compared to a fascist regime assembled by a Roman Otaku. However, it's not like they rib on leftism outright, in the same way Fallout 2 shits on the right, they just show you that the realities of the world might not be the most favorable towards liberal democracy.
I suppose that's why I like them both so much.