[1] https://www.usnews.com/news/best-countries/articles/2017-06-...
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.
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.
Which puts us in solid agreement, but you're foolish if you think this doesn't seriously advantage countries that are capable of maintaining agreements over the USA.
That isn't a hypothesis you want to stress-test, though. "My reputation survived the last great gaffe, therefore it will survive the next one" is a very poor long term gamble.
It lost the war, but that's not the same thing as just walking away frivolously, on whim.
Basically, the rest of the world will have to learn that getting the US to agree to something that is opposed by a significant group of Americans is a losing proposition. The fact that the Paris climate pact was not even submitted for ratification by the Senate, should tell you that there was significant opposition.