The ex-Prez -- who just survived an assassination attempt over the weekend -- popped up in Milwaukee for night #1 of the convention ... marking the first time he appeared at a public event since Thomas Matthew Crooks tried putting a bullet in his head Saturday.

Of course, since then ... everyone has been saying his security detail would be beefed up -- including President Biden, who dedicated more protection -- and that was apparent Monday.

Take a look at this video that was posted by the Trump campaign ... it shows DT arriving at the RNC with a throng of Secret Service agents around him, flanking him on all sides and moving in unison with him as he made his way up the stairs to his elevated seat.

What people are noticing about the makeup of his Secret Service detail now, however, touches on something many have been commenting on since this weekend ... namely, the fact some feel like the prominent female agent with Trump on Saturday was out over her skis.

It's a pretty harsh characterization, frankly -- with a handful of folks zeroing in on video of her seemingly fidgeting with her gun after DT had been shot, and apparently looking frazzled -- and you can even argue it's outright sexist ... and yet, many were critical of her regardless.

It's unclear if the fact there were no female agents around Trump Monday night is a direct result of the scrutiny -- but it is something folks noticed ... and very well may be a choice.

The thing is ... this wouldn't be something the Trump campaign or even Trump himself would decide on -- it would be something directed by the Secret Service itself, and we should note ... the current director, Kimberly Cheatle, is a woman.