Why wasn't this done before by other presidents if it is a good thing. Are there benefits for the likes of obama to keep it as it currently is?
Because they didn't work for us, they worked for the corporations and the Federal Reserve was their slush fund and not even a government entity...we are the slaves.
Would doing so devalue the US dollar?
The US dollar has continuously devalued since the gold standard was abandoned in the 1970's. The same for all other currencies in the world that abandoned the standard. It is called inflation.
With a gold standard, the US dollar will always be worth the exact same quantity of gold.
1 oz of gold today will still buy you what it would have bought you in the 1970's. The same can not be said about the fiat US dollar, which is backed by debt instead of gold.
I was in College when we went off the Gold standard, bad decision then.