Ukraine: When does the Budapest Memorandum go into effect and how? Is a "memo" a congress. treaty?

See subject. From Wiki cite (surely not original text of memo):

US,UK,Russia to Ukraine: Give up your nukes.
US,UK,Russia to Ukraine:
[li]to respect Ukrainian independence and sovereignty within its existing borders;[/li][li]to protect Ukraine from outer aggression and not to conduct aggression toward Ukraine;[/li][li]not to put economic pressure on Ukraine in order to influence her politics;[/li][li]not to use nuclear arms against Ukraine. [/li][/ol]

I am not a diplomat but I’m not seeing any language that requires the signatories to protect Ukraine from another power. They all agreed they would each not invade Ukraine but there doesn’t seem to be any requirement to act if one of the powers (like Russia) decides to violate the treaty. The signatories are merely required to consult each other if one of them violates the terms.

Here’s the full text.