[WS:] The way you posed these questions indicates the crux of the problem - namely that the left has become reactive rather than proactive and merely reacts to the initiatives of the right. As a consequence it is forced to fight battles on the terms defined by its enemies, which is not a winning strategy imho. The left has stopped thinking progressively long time ago - it merely reacts to capitalism by critiquing it and occasionally staging protest actions against initiatives taken by the right. In way, the left became a rear guard fighting against what is being sold as neo-liberal "progress."
"What is to be done" in such a situation? First, let me tell what is NOT to be done. First, I do not subscribe to the view offered by Shane, Carrol, et. al suggesting that the Democrat party "function" is to disarm the left. This is plain delusion of grandeur of people who fell into insignificance long time ago and still do not know what hit them. The main "function" of the Dem party is the same as that of any political party anywhere, to win elections and to dispense political patronage to those in a position to pay for it. Believing that its function is to kill the popular initiative of the left is like believing that the main function of the trucking industry is to run over deer on interstate freeways. In reality, both the self styled radical lefties and the deer are minor annoyances that are simply run over in the course of doing business. The Dem party is not left's friend or even representative, but it are not the left's enemy either. It is a force that self-delusional lefties imagine that should be their friend and then they get pissed when they caught, like deer, in its lights.
Quite frankly, "direct action" (such as protests, strikes, demos, etc.) have little tactical and zero strategic effects. It is purely symbolic, ritualistic activity that, like magic rituals, does not change anything in material reality and only gives those perform it a peace of mind that they did something to avert a calamity. Pursing this form of action for political gains is pretty much wasting one's resources.
To know what "is to be done" we need to state the main reason why the left has so little political influence in the US, even within the Dem party. This reason is the winner take all electoral system, which forces the parties to converge in the "center" - which in the Us is pretty much to the right. It's been know for ages as the Hotelling's law - look it up http://en.wikipedia.org/wiki/Hotelling's_law.
So the question should be phrased as "what a minority (such left wingers) should do in a majoritarian winner-takes-all politics? The answer is rather simple - change the electoral system to get access to political offices. Instead of fighting shadows on the wall of a Platonic cave (which includes anything from global fight against abstractions such as "neo-liberalism" to freedom for Tibet) - the left should focus on a single goal - implement proportional representation.
There is nothing in the US constitution that prohibits its implementation, and there are many groups that do not subscribe to a left political philosophy, but will certainly embrace the idea of proportional representation.
I understand that PR would not do much to embattled public sector worker in Wisconsin - but at this time the best that these people could do is to cut the losses and withdraw to new strategic positions.
Fighting the blitzkrieg of the right head-on makes little sense, unless the defenders have the capacity of drawing the enemy in and slowly degrading its blitz by attrition. Clearly, unions and the left do not have that capacity, not even close.
So the goal to be achieved is strategic not tactical at this moment. That means no attempt to score quick electoral victories (this includes the third party nonsense), no protest action against initiatives of the right, but instead working with the forces that share the same strategic objective - change of the electoral system. Yes, that means working not only with Democrats, but also with some unsavory characters of the right. The level of public disgust with the Republicrat doupoly is such that electoral reform should not be a very hard sell to people who feel abandoned by the existing party system.