Does the stock market traditionally drop around election time? Uncertainty is usually bad for the market, yeah?
[0]: http://www.marketwatch.com/story/how-the-stock-market-tends-...
The loss of our reserve status and the gradual divestiture of USD assets by foreign central banks would have the impact (if gradual) of raising long term borrowing costs, lowering asset prices and increasing wage pressures. Those effects would be uneven across the economy and benefit some people at the expense of others. Generally helping the factory working I Ohio and hurting those who own highly leveraged assets (like US stocks).
Most of the benefits of the USD simply accrue because of the size of the US economy which tends to make it less volatile and less prone to "runs" on the currency. Even if the world were to panic about the direction of the US political system there simply isn't anything else big enoug to run to that would seriously tank the dollar. The same cannot be said for the political developments in a counrty the size of Venezuela.
These benefits are independent of the reserve status and accrue to the Euro just as much as the USD.
edit: and let me clarify, because you misunderstand me. The size of the US economy is one thing, but the stability of an ally's political system and leadership is another. The UK and the US have taken hits that will play out over a long term and are not easily reversible, at a time when the alliance has serious challenges and very capable adversaries.