http://www.independent.co.uk/news/world/americas/us-politics...
So, not 70% of his supporters, especially considering not all Republicans voted for him, and some Democrats did.
And the math is funny anyway. I haven't seen recent registration numbers, but last I looked, it was roughly 1/3 Democrat, 1/3 Republican, and 1/3 unaffiliated. It might be 40%, 30%, and 30%, not sure; the point is that I seriously doubt 70% of the people who voted for Trump support the Paris treaty, and certainly this article does not say that, though it tries very hard to imply it.
The not-being-responsible-for-other-countries bit is also a popular policy of his (arguably, its his most widely-appealing position altogether), but I'm confused that you think that that applies to the Paris accord. The accord didn't mandate us giving anyone else anything, and climate change is going to mess the U.S. up as much as anywhere else.
And part of Trump's message was that the U.S. shouldn't be the guarantor of the security of the rest of the world. That was a hugely popular proposition with his supporters.