This tweet from @SenJohnMcCain received a barrage of spammy replies crammed with as many hashtags as possible. There's some variety, but all seem to contain #opmayflower2018. (Thanks @Shaun7559 for the tip.) 
Looking at replies to McCain containing #opmayflower2018 results in 4808 tweets (including retweets) from 397 accounts; 983 original tweets from 47 accounts. The activity started at 6:30 PM Central on 5/11; volume is high for a little over an hour.
This table shows the frequency of the various hashtags included in the #opmayflower2018 tweets. We'll come back to the ones highlighted in blue (cyan?) later.
Our initial suspicion upon seeing these tweets was bots. Interestingly, common indicator of automation such as round-the-clock activity and usage of non-Twitter apps/service is entirely absent.
While looking over the accounts that participated in this campaign, we found an interesting tweet containing links to a Facebook page. What's there to find on the other side?
On the FB page are instructions for how to carry out the op. Step 4 is of particular interest - it would appear the organizers of #opmayflower2018 are trying to make it more difficult for Twitter to identify spammy posts via duplicate image files.
Returning to the list of hashtags, several of them appear to represent the team assignments referenced in the Facebook post. It's also possible these hashtags are being used to track the reach of tweets from each group.
Retweet network for #opmayflower2018. The major nodes are all connected to one another, which aligns with step 7 of the FB instructions (everybody RT everybody else's tweets). These accounts are not bots, but they're doing a damn good impression.
Much appreciation to @ZellaQuixote for various research aid with this thread.
Exactly five minutes ago (6 PM central) my notifications shot up to 99 instantly. Pretty much all of them look like this. It would appear to be a sequel to the spam campaign targeting McCain, with @MaxineWaters as tonight's target.
The methodology seems to be the same too - they're all retweeting each other's tweets. Apparently this thread was interesting enough that I deserved to be included in the mentions alongside James Woods and Alex Jones.
Each of these screenshots was taken within 10 seconds of checking my notifications.
Much like the campaign targeting McCain, there are a few variants of the tweets at Waters. Here's a different one.
There are also some targeting @RepAdamSchiff.
27 minutes in, and the vast majority of the notification spam I'm receiving consists of retweets rather than original tweets.
Another addition: @NancyPelosi. Also note that the list of targets who are mentioned (as opposed to replied to) is different than in the McCain iteration of this campaign.
I'm keeping an eye on the tweet volume as this proceeds - so far, at least 11114 tweets (including retweets) have been sent as part of this campaign. @SeanSpammity
I've now received at least 21785 notifications in a little over an hour. Twitter's spam policy would appear to apply.
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We decided to explore the assignments in more detail. These tables show which groups "A = #TeamAlpha, etc) used which hashtags and tagged which accounts on 5/10 (the replies to McCain's tweet). There's some variance in the hashtags, but all tagged the same accounts. @ZellaQuixote
Same figures for tonight's (5/12) spam campaign. There's substantially more variety in the assignments this time around.
Finally, here are the assignments from both nights combined.
