The emerging conventional wisdom is that, with the selection of Paul Ryan as Romney’s running-mate, the 2012 election has suddenly become a serious matter. Rather than a purely negative campaign, the GOP is aiming for a mandate – a higher-risk, higher-reward strategy. And the Democrats are aiming for a counter-mandate, to bury the Ryan budget once and for all. Whichever side wins the election, the ship of state will be set on a definitive course for years to come.

But I suspect the conventional wisdom is wrong. The structure of American political institutions and norms makes it extraordinarily difficult for either party to seriously turn the ship of state. To enact major reforms requires either a substantial majority or at least some cooperation from the party out of power. The former is not likely, for either party, and if post-election an incentive for the latter is to emerge, I’d like to know what it is.

Let’s take a trip down memory lane, to 2008. The Democrats controlled both the House and the Senate, with large majorities, and won the Presidency with the largest percentage of the vote achieved by a Democrat since 1964. It was the clearest “mandate” election since 1980. And what happened? The GOP responded by declaring a policy of wall-to-wall obstruction, which, if not perfectly enforced, came pretty close. And the Democrats, faced with that obstruction, had to consider what the impact of a series of party-line votes would be on their most marginal members. The result was legislative triage: we got a catch-all stimulus bill, and an insurance-company-friendly version of health-care reform that passed by a whisker. And this was followed by a massive Republican tide in 2010.

Suppose Republicans take the Presidency and both houses of Congress in 2012. The largest plausible Senate majority will fall short of being filibuster-proof. The largest plausible popular vote majority will fall short of Obama’s victory in 2008. If the Republicans interpret their victory as a mandate, that means trying to pass major changes to core entitlements, large upper-bracket income tax cuts, large cuts in discretionary spending (apart from defense), and the elimination of tax deductions popular with the middle class. Why would the Democrats cooperate in passing any of this? Why wouldn’t they adopt the kind of wall-to-wall opposition that characterized the Republican opposition after 2008?

Perhaps they couldn’t whip their members as effectively as the Republicans did. But if the Democrats suffer large losses in the Senate, their caucus – like the Republican caucus in 2009 – will have shifted left, and will contain fewer members vulnerable in a general election. Moreover, 2014 will be a midterm election after a change in party in the White House, which typically means that the incumbent party loses seats. Democrats will, precisely because of defeat, be more unified, and will feel they have the wind at least somewhat at their backs. And they wouldn’t have to whip quite as effectively as the Republicans, because a 2013 Republican majority in the Senate, under any plausible scenario, will be smaller than the Democratic majority was in 2009.

And the stakes, for the Democrats, couldn’t be higher. What, exactly, does the Democratic Party exist for if it votes for upward redistribution of wealth through the tax code, privatization of Medicare, block-granting Medicaid, and gutting domestic discretionary spending? If they can’t stand united in opposition to that kind of agenda post-election, the party would simply collapse from lack of rank-and-file support.

But what if the Democrats win? What if President Obama wins a solid reelection victory of 3-4 points, the Democrats retain a thin majority in the Senate, and make gains in the House. That would be a clear repudiation of the Ryan budget’s priorities. Clearly, the Republicans, post-election, would have to reconsider those priorities, and work with the new Democratic majority on common goals.

Or, you know – not. In the worst-case-scenario for Republicans, they won’t have lost a huge amount of ground. It’s unlikely they’ll lose the House, and they are very likely to make gains in the Senate even if they don’t gain a majority. They will certainly have lost winnable seats in both the House and the Senate that can be attributed to having chosen candidates that were too conservative – but that was true in 2010 as well, and those losses don’t seem to have changed the priorities of the Republican electorate. This Congress has the lowest approval rating in recorded history. If most incumbents survive an election held under those circumstances, what’s their incentive to change their behavior?

Moreover, the Republican Party’s entire identity in the age of Obama has been oriented around opposition. The party’s leaders have told their members that they are the only thing standing in between the administration and the destruction of America as their members know it. They can’t simply change their tune because they lost an election. They will have to continue to fight the good fight – for the sake of the country. What else are they going to say – “the American people have spoken, and they have chosen Socialism?”

We do not live under the British constitution, where an electoral dictatorship can pretty much do whatever it wants, constrained only by the knowledge that there will be another election that could devastate them if they don’t deliver the goods for the people. The American political system requires either a very large majority or a high degree of receptivity to cooperation to enact major legislative changes. The median voter theorem dictates that large and stable majorities should be very hard to assemble, while the successful ideological and demographic sorting of the parties has made cooperation much more expensive. The result is a system that frustrates accountability. And, since accountability is risky for incumbents, the current system serves the interests of a stable majority of legislators.

The battle is indeed joined, and it does represent a sharp contrast of visions in terms of budget priorities. And yet, in terms of tangible consequences, it may yet be as Fortinbras’s captain said of his impending battle with the King of Poland:

Truly to speak, and with no addition,
We go to gain a little patch of ground
That hath in it no profit but the name.