The old Article 3:

The Union shall be served by a single institutional framework which shall ensure the consistency and the continuity of the activities carried out in order to attain its objectives while respecting and building upon the acquis communautaire.

The Union shall in particular ensure the consistency of its external activities as a whole in the context of its external relations, security, economic and development policies. The Council and the Commission shall be responsible for ensuring such consistency and shall cooperate to this end. They shall ensure the implementation of these policies, each in accordance with its respective powers.

The old Article 3 is renumbered 4 and replaced with this:

Article 4 - Relations between the Union and the Member States

1. In accordance with Article [I-11], competences not conferred upon the Union in the Treaties remain with the Member States.

2. The Union shall respect the equality of Member States before the Treaties as well as their national identities, inherent in their fundamental structures, political and constitutional, inclusive of regional and local self-government. It shall respect their essential State functions, including ensuring the territorial integrity of the State, maintaining law and order and safeguarding national security. In particular, national security remains the sole responsibility of each Member State.

3. Pursuant to the principle of sincere cooperation, the Union and the Member States shall, in full mutual respect, assist each other in carrying out tasks which flow from the Treaties.
The Member States shall take any appropriate measure, general or particular, to ensure fulfilment of the obligations arising out of the Treaties or resulting from the acts of the institutions of the Union.
The Member States shall facilitate the achievement of the Union’s tasks and refrain from any measure which could jeopardise the attainment of the Union’s objectives.

The point one of this new article is a formulation of the principle of conferral. The principal of conferral in my view is an other point that makes a federal Union to be distinguishable from a unitary State with very strong regional autonomies. In the second case every power not explicitly given to the regional institutions by the unitary constitution will belong to the central institutions. Federal Unions instead are based on the principle of conferral: every power not explicitly given to the central institutions will belong to the regional ones. The principle of conferral “always underpinned the European Union“, even if only now it has been stated explicitly, and in my view resembles very much the Tenth Amendment to the United States Constitution.

The whole Article 4 anyway aims to remark the reciprocal “rights&duties” between European Union and Member States. Again this is quite normal in any federal Union, in which some powers are explicitly conferred to central institutions and all other powers belong to the regional institutions. So even if on a mere abstract level there is no difference among EU and a federal Union, of course there is a big concrete difference: national security is “the sole responsibility of each Member State”, that has to be added to the repealing of the common defence as an objective of the Union (see here).

So the legal framework of the European Union seems to me to be clearly a federal one:

• there is a set of regional entities,
• these regional entities agree to give rise to a new central level and to confer some explicitly defined powers to it,
• what is not explicitly conferred to the central institutions remains to the regional entities,
• the regional entities has not to be abused by the central institutions.

However even if the general structure of power division is that of a federal Union, if we look at the way how power is actually divided we find a huge difference among the European Union and for example the United States: the Member States of the EU didn’t conferred to it the military power, so it seems there will no room for a common defence (at least at this point of the treaty, but we will see that things are a little different).

Anyway, as my last remark I want to notice that “national security remains the sole responsibility of each Member State” is a little ambiguous statement if we look at it in order to answer this question: if a group of Member States will decide to create a common army the European Union shall block them? I mean, the assertion that national security is just a matter of the States can be read also as forbidding a sub-set of the Member States of clustering together on this point?

The answer to this last question will come later in the treaty.