Doug Bandow makes his case against bringing Montenegro into NATO:

The only argument for Montenegro’s inclusion that has any logic is to signal that the alliance is continuing to accept new members, no matter how irrelevant and insignificant the country.

There is no compelling reason to bring Montenegro into the alliance. The reasons not to bring them in are many. The alliance gains nothing from adding a new member. Most of the people in the country are opposed or indifferent to joining. Montenegro’s government doesn’t meet alliance political standards for new members. Another round of expansion just makes an already unwieldy organization even more so. Adding Montenegro doesn’t expose the alliance to the risk of a major war, but that is because the country isn’t threatened by any of its neighbors and doesn’t need the protection that the alliance affords. Neither the U.S. nor the alliance is made more secure by adding a new member, and enhancing our security is the only reason why we should take on another ally.

The main reason that advocates for continued expansion want Montenegro in the alliance is that it keeps the idea of expanding NATO alive, and the other reason is that it irks Moscow. Neither of these is a good reason to extend yet another security guarantee to a country that won’t pull its own weight and will contribute virtually nothing to the alliance. It would have been better if the offer of membership had never been made, but there is still time to withdraw it.