And he's not the first leftist to declare that a specific part of the Constitution that impedes his intended agenda is no longer relevant, although specifically attacking the "Natural Born Citizen" clause in this fashion is something kind of unique to the Obamatons.
Efforts at deligitimizing the Constitution by pronouncing disagreeable pieces of it "archaic" or inapplicable to the current day - as an alternative to pursuing much more difficult amendment process - were common throughout American history. Franklin D. Roosevelt did this with the "interstate commerce" clause, describing it as a relic of the horse and buggy era, because it (temporarily) put limits on congressional power to control the economy by enabling the SCOTUS to nullify some of his New Deal legislation as unconstitutional.
In many ways, the Obama era is a rerun of the 1930s. Not so much a coincidence, but because the intellectuals in the Obama camp are well aware of that earlier era and have a similar policy approach, especially on the economy.
He is the arbiter of what is and is not relevant, I suppose. If it’s no longer relevant, why not amend the constitution? Because he knows such an amendment would have no chance, because the political consensus is that it is relevant?