I would advise caution against this. You don't want Ukraine to become the start of World War III. At the same time, there's so much more that we can do to help Ukraine to reach out through the partnership for peace program and other activities to make Ukraine more secure. I don't advise giving Ukraine article 5 protection, but at the same time we should be doing much more to enhance their security.
On November 1st, 2017. See this statement in context.