When it comes to Keynesian theory, the goal is to run a deficit and then turn around and earn it back after the recession. Before we were using a balanced budget. Do you think that since US presidents only serve 4 year terms, with a two term maximum, thus having no incentive to conserve for the future, plays a large part in Keynesian theory not working the way they expected it to? Or does it really come down to the faulty principle of savings=bad? What's the largest fault of the policy?
It certainly is easier to blame on on the guy that came before you, and easy to leave it as the next guys problem. The problem you described is only worsened when you consider how frequently lower offices are voted in and out of office, further increasing the short-sightedness effect. The Keynesian diagnosis that savings is bad, doesn't crowd out private investment near as much as "spending=good" does, so I typically don't blame Keynesian policies failures on that theory. The largest fault of Keynesian economics is that it is central planning, which FA Hayek and Ludwig von Mises pointed out is doomed to fail since central planners cannot decide where resources should go anywhere near as individuals can.