by system failure
It is certain that various US think tanks will be monitoring right now the rise of the Left in Greece with the radical-Left party SYRIZA, as well as Podemos in Spain and other countries in Europe (http://failedevolution.blogspot.gr/2014/11/signs-of-resistance-against-neoliberal.html).
It's quite remarkable that the US political system, especially after Clinton administration, has been adopted by Europe, with the transformation of the Social-democrats. A characteristic example is Greece, as the Socialist party PASOK under Kostas Simitis, implemented the neoliberal perception of the free market and the financialization of nearly every aspect of economic activity.
However, as in the US the Left was demonized for decades and totally vanished from the political scene, Europe was meant to be the field of the new Leftist political powers, after the latest global financial crisis. Inevitably, any possible change will start from Europe and follow a reverse direction of that of neoliberalism in the early 90s.
Therefore, a first potential consequence would be that such a possibility could become a good example of an alternative political solution against the bipolar plutocratic political establishment in the US, which was enhanced rapidly after Clinton administration in the early 90s, secured big capital's interests and left no choice to the majority of the American people to vote for their interests.
A second consequence for the US deep state would be the loss of Europe in the new Cold War. Except from Britons, who have traditional deep ties and common interests with the US, the rest of Europe could slip to the Sino-Russian bloc which grows rapidly in the military and economic field and increasingly gaining independence from the Western economic system, attracting other countries too. (http://failedevolution.blogspot.gr/2014/08/a-perfect-timing-for-argentina-to.html)
A third consequence would be the abrupt termination of the Greek experiment and its deployment in Europe and the US. This could trigger a reverse situation against the accelerated expansion of the neoliberal doctrine* in its most extreme version as a forerunner for the new global Feudalism.
Plutocrats will do whatever necessary to buy more time. The war already started in Europe. The systemic establishment in Greece try to present SYRIZA as a non-serious political power and downgrade the rapid change of the Greek and the European political scene especially after the latest euro-elections. At the same time, current government is ready to collapse and therefore already tries to force the Left to compromise and agree on the catastrophic measures imposed by Troika. SYRIZA, of course, refused to do this and asks for immediate elections.
Post-WWII history shows that the United States tried to prevent the rise of the Left in Europe during the whole period of the Cold War, because of the fear of the Soviet further expansion. This was done through provocative operations against Leftist organizations (Gladio in Italy) (http://failedevolution.blogspot.gr/2014/10/an-example-of-provocative-operations-in.html), or, by supporting dictatorial regimes (junta in Greece) (http://failedevolution.blogspot.gr/2014/04/black-anniversary.html), etc. Surely, the US deep state will try to prevent a domino of rise of the Left in Europe, for one more time, as this will probably bring serious trouble to the economic elites both in the US and Europe. The propaganda by the mainstream media already started.
All these scenarios, however, could also make neocons even more anxious to impose their lunatic plans to provoke a general conflict with Russia as the only alternative against the dramatic shift of the global geopolitical balance, unless we see a fast creation of a corresponding political power in the US inspired by the European Left. It would be even better if such a power could rise from the movements in the streets (Occupy movement, etc.), like Podemos in Spain.
A unified Left could trigger rapid changes globally against the neoliberal expansion, destroying plutocracy's plans for total domination. Of course this would require to remain ideologically pure, not to be transformed and absorbed by the neoliberal perception like Social-democrats. Οtherwise, the new political gap could trigger unprecedented and uncontrolled, chaotic situations, in the absence of any other political alternative that could fill it.
* According to these plans, the ultimate goal would be probably to dissolve the vast Russian territory in future and bring in power Western-friendly puppet regimes, in order not only to conquer the valuable resources, but also to impose permanently the neoliberal doctrine on "unexplored" regions and populations.