Once given, can a NATO member withdraw or cancel its ratification of an Accession Protocol for a candidate member?

Question

The Accession Protocols to the Washington Treaty for Finland and Sweden have so far been signed by 28 of 30 NATO members. Once all NATO member countries have notified the Government of the United States of America (the depository of the Washington Treaty) of their acceptance of the protocols to the North Atlantic Treaty on the accession of the potential new members, the Secretary General invites the new countries to accede to the Treaty.

My question is, Can a NATO member, once it has ratified the Accession Protocols for candidate members, withdraw or cancel that ratification before the Secretary General invites the new countries to accede to the Treaty?

The background to this question is: I am participating in a forecasting tournament. The question I am trying to answer is, "What is the probability that Finland and/or Sweden become members of NATO before 1 July 2023?". My answer largely depends on the actions of Hungary and Turkey. I am wondering, however, if I can rule out the withdrawal/cancellation of any ratifications that are already given.

Answer 1

The NATO treaty does not seem to explicitly answer this question. However, the following may be relevant:

Article 10 of the NAT:

The Parties may, by unanimous agreement, invite any other European State in a position to further the principles of this Treaty and to contribute to the security of the North Atlantic area to accede to this Treaty. Any State so invited may become a Party to the Treaty by depositing its instrument of accession with the Government of the United States of America. The Government of the United States of America will inform each of the Parties of the deposit of each such instrument of accession.

As per this, unanimous agreement is the basis of accession. Even a unilateral withdrawal of ratification would violate unanimity.

Also, consider this:

The governments of NATO member states ratify the protocols, according to their national requirements and procedures. The ratification procedure varies from country to country. For example, the United States requires a two-thirds majority to pass the required legislation in the Senate. Elsewhere, for example in the United Kingdom, no formal parliamentary vote is required.

Once all NATO member countries notify the Government of the United States of America, the depository of the Washington Treaty, of their acceptance of the protocols to the North Atlantic Treaty on the accession of the potential new members, the Secretary General invites the new countries to accede to the Treaty.

They do not supply a mechanism for reversing ratification. However, the ratification procedure is entirely upto the country and its constitution. Hence, if some country's law provides for reversing ratification, I suspect NATO will have to respect that given the inherent ambiguity in the treaty text regarding this - especially considering that NATO works on unanimity.