I have some quibbles around the margins of your comments.
The national debt in absolute dollars continues to increase year after year and that is NOT sustainable regardless of current debt to GDP levels.
I totally disagree. I think the absolute level of national debt is irrelevant: it's only the ratio of that debt to GDP that matters.
There is nothing Keynes him self said that approves of deficit spending through economic boom times or the maintenance of ANY level of long term national debt.
I've never heard that, and I'm not doubting it is true, however, if so that would be one of the major mistakes which Keynes, like Einstein, made in an otherwise inspired body of work. I see no evidence that advanced economies cannot comfortably and indefinitely maintain debt to GDP ratios up to about 50%, and if the economy is not being severely mismanaged, probably up as high as 70%.
The main question is what purposes that debt is put to. If the US had been devoting its deficits to things like adequately upgrading its transport infrastructure, even at current levels it would not entirely be a bad thing. It did nothing like that. The net effect of its debt has been to rob future retirees and welfare recipients, Peters, to fund excessive consumption by those in the past and current day, Pauls. :-(
There can be no doubt, as it currently functions, the "third rail" of US politics, its Social Security system, is unsustainable. And this IS NOT because its "Trust Fund" is on course to run out in a few decades time. That fund is significant to the political debate, but it has NEVER had any tangible effect in the real economy (beyond modifying the effective rates of income tax individuals must pay). It is a complete fiction. AFAIK, everything paid into it comes straight back to the government as the fund is obliged to invest all of its "assets" in Treasury bonds. Nothing would change if it was legislated out of existence and the Federal government began paying retirees itself from its general coffers!
Germany has a similar fund, but they bit the bullet when it became obvious the fund was on course to run out. The fund cut the rates of benefit payments to retirees to maintain its viability. I don't know if their fund has the freedom to invest contributions it received as they see fit. I presume they do. Without that, if such funds can only invest in government bonds, they may as well not even exist.
In contrast, the benefits the US Social System are currently paying out are effectively "tied to train tracks" at the moment - just waiting for the "locomotive", intractable gridlock within Congress, to smash into them. Unless ways are found to cut those payments, reducing the maximum level of payments or increasing retirement ages, budget deficits will blow out to an extent that the US will follow Japan down the path they are on.