It's not a *parliamentary* democracy, and many here will say instead that it's a republic, and yes, in many ways it was based not on the Greek idea of democracy, but is more related to the Roman republic. Unfortunately, the Roman model seemed to reward ambition more than populism...and the American model seems to do the same.
That being said, I've maintained since Trump's election that America is indeed in decline (and that China is ascendant). It makes me think of nothing more than Kipling's motive for writing "White Man's Burden", in which he heralded America's ascendancy and the decline of the UK.
But not all hope is lost. I know that it sounds corny, but I wrote a reply to Kipling's poem, and I'm inordinately proud of it. I encourage you to read it here.