1) Growth alone isn't unsustainable. Lot's of people say the market is overvalued. A reasonable counter argument is that there is a lot of capital looking for somewhere to go. Demand for investments with a decent return increase the prices of those investments. Meaning the markets aren't overvalued.
From a macro perspective, aggressive income redistribution would both benefit the entire economy and stabilize stock market prices, pushing capital into households and away from institutional investors.
2) The market gives no ***** that there are 30 people running for President. The market (and any person with a brain) knows that only a few have a realistic shot at the presidency--just like every other election.
But if you truly know that the Dow will dip down to 11,000 soon, there are many ways for you to become very rich between now and then. I suggest you get on it.