What is a political "argument"?

Questioning whether the Tea Party can be effectively countered by argument, DiA, I think, whittles away its (his?) own premise:

...do intelligent arguments make a difference? I'm trying, and failing, to think of an instance where voters on any side have been persuaded by a reasoned opposition on any issue. It might happen with individual voters on particular issues, largely of the technical variety—if someone sits down to figure out whether they support a bond issue, maybe—but I can't think of a single issue where an argument, however elegantly expressed, has tipped the balance. These, I think, are the methods by which public opinion may be moved:

• A momentous event (9/11, the oil spill, a botched execution)
• The gravitational pull of mounting social change (gay marriage)
• A timely and effective message, repeated ad nauseam ("It's the economy, stupid;" "change")

Nothing against ideas, but their effect seems to come after they trickle down (as in the messaging method described above), or if they have the fortune to hook on to a current event. It does seem that individual politicians can benefit from having lots of good ideas (Barack Obama, Bobby Jindal), but it seems like the political gain from that is, "that guy's smart", rather than "after careful consideration, I agree with the content of his platform.

Sullivan finds these postulates depressing  But do they boil down to much more than "arguments don't occur in a vacuum"?  I don't think that the causes of shifting opinion that DiA outlines suggest that "argument" has no effect.

Momentous events may ultimately settle arguments, for instance by discrediting Hooverian retrenchment in the face of Depression. Successful politicians articulate what's not working, and why -- though sometimes, for sure, cleverly packaged nostrums win the day, short-term. "The gravitational pull of mounting social change" is shaped gradually by event and argument - as in the spectacle of Martin Luther King's peaceful demonstrators being beaten and having debris heaped on them -- and also eventually captured by effective argument, as in the California court these recent weeks on gay marriage (Judge: whom does it hurt, and how? No answer...).

As for "timely and effective messages," Bill Clinton's and Obama's worked because they were backed by policy prescriptions credibly purporting to address current problems.  For Obama, these were various economic supports for the middle and working classes combined with restored taxes on the wealthy; passing universal health insurance; ending the war in Iraq and refocusing on Afghanistan (oy...).  I have attempted elsewhere to document that Obama's campaign speeches, far from consisting of soaring but empty rhetoric, generally offered a strategic and conceptual framework for a set of policy specifics.

Which is not to say that DiA is wrong to suggest that the effect of such prescriptions may have more often than not been to make voters think,  "'that guy's smart', rather than 'after careful consideration, I agree with the content of his platform.'"  I am not denying the mechanisms that according to DiA impact public opinion -- I just don't see them neatly cut off from some Platonic ideal standing in for "argument." Ultimately, in a democracy, successful or failed policies more often than not themselves become decisive "arguments," articulated by successful politicians.

P.S. it occurs to me, xpostfactoid, that I'm in some sense perhaps channeling Jonathan Bernstein here, who  takes an often bracingly utilitarian view of the way politicians respond to electoral incentives, the strongest of which is ultimately (in the long run, if they last long enough) policy success.