By Mike Dorf
With Ireland's "yes" vote, the Treaty of Lisbon now only awaits final action by the Czech Republic and Poland to become effective. The impact of full ratification on the EU and its member states is not yet known (though I share the general view of most Europeans from the center left to the center right that this is a step forward). Here, however, I want to say a few words about the ability of states (whether nation-states or states within a federal union) to vote a measure up after they have voted it down.
I'll begin by noting an oddity. Under the current EU framework, it is not 100% clear that a member state can withdraw. The Treaty of Maastricht has no withdrawal mechanism, and pursuant to the Vienna Convention on the Law of Treaties, a treaty party can only withdraw from a treaty by invoking a withdrawal mechanism in the treaty or by mutual consent of the signatories. (Since 2006, Ireland has considered itself bound by the Vienna Convention.) Under Article 56 of the Vienna Convention, a party can withdraw from a treaty with no express withdrawal mechanism if the nature of the treaty admits of a right to withdraw, which is probably true of the EU. But perhaps it isn't true. Perhaps the EU currently creates, as the U.S. Supreme Court said of the U.S., an indissoluble Union. In that case, then, oddly enough, by ratifying the Treaty of Lisbon, Ireland makes it easier to withdraw from the EU, because once fully ratified, Ireland and other member states will have a formal right to withdraw from the EU.
Okay, so that's an oddity. No one is suggesting that Ireland was about to withdraw from the EU. But note that Ireland got to vote yes after voting no even though it would not have had the opportunity to vote no after voting yes. That is, once the Treaty of Lisbon is ratified, no member state can say it wants to go back to the pre-Lisbon version of the EU. That asymmetry looks problematic. Why should a yes vote supersede a no vote when a no vote can't supersede a yes vote?
The answer, I think, is that the yes vote is supermajoritarian while the no vote is not. To be sure, to ratify the Treaty of Lisbon, only a majority in each member state's plebiscite is required. But unanimity of simple majorities is tantamount to a very strong super-majority requirement. So the asymmetry of yes-after-no-but-not-no-after-yes is justified by the fact that it's so much harder for the EU as a whole to vote yes than it is for any single member state to vote no. The option of a one-way Irish "do-over," in other words, was not simply a way to stack the deck in favor of ratification.