Is now the time when a third party can replace either the Democratic or Republican Party?

Third parties generally emerge when some sort of major
change makes the previous party system impossible to maintain.  For example, it was the
splits between the North and South leading up to the Civil War that led to the death of
the Whig Party and the eventual creation of the Republican Party.  So the question then
becomes whether there is such a major change taking place
today.

One can certainly argue that there is.  The rise of
the Tea Party and of anger about government spending and taxes (while at the same time
people demand that their Medicare and Social Security not be touched) is putting a great
deal of stress on the political system.  Neither party seems at this point to be able to
come up with a way of satisfying voters that seems likely to be workable and
long-lasting.  In such an environment, with the US population aging, globalization
increasing, and questions arising about the role of government, it could be that the
time is ripe for a third party to arise.