This business of calling every scandal under the sun “something-gate” is a practice that ought to stop. It does nothing to help educate people about the issue, and does much to trivialize whatever issue it is trying to convey.
Watergate was the name of an important part of the case that lead to the resignation of Richard Nixon.
Take “Memogate” - in this case, I think it would be more important to remember the details of what this case is really about, rather than some slogan that refers to another time in history when a president of the US was being impeached for completely unrelated - and I’d say less serious - charges. There is no reason why we shouldn’t expect people to learn and remember the details and importance of “Downing Street Minutes” scandal.
BTW, you can find more information about the Downing Street Minutes scandal here.
Here’s an interesting summary of the original Memogate.