No. I'd take this twitter post with a huge rock of salt.

First, he posts a video of AF1: since this is an emergency situation with strict security control, he would probably not be allowed to film and post this anyway.

Second, the clip is way too short to verify any other details than "AF1 is preparing for take-off": who's to say that this wasn't taken during a more peaceful time when a reporter got carried away at being so close to AF1?

Third, the language of the tweet itself is suspect. Who writes "Due to security issues" to describe a threat to the family? Why would they then publicly post that there's a threat anyway? Then there's "the president Trump".

Fourth, the #tags are not separated.

Fifth, the account name is poorly formatted. It should not be identical to the twitter handle if it were a professional account.

Sixth, the name itself. Rabert is a rare Scots form of the name Robert, and Petrosian is an Armenian surname. These are two very disparate combinations and would make this a very unique if not unlikely name. A Google search for Rabert Petrosian produces very few results (less than 2000) for someone hired to be WH journalist. There are, however, over a hundred thousand hits for "Robert Petrosian".

Finally, and more likely, there's the possibility that a foreign agent is ghost-writing for an non-existent person. This person demonstrates a poor understanding of the English Language. I'm suspecting that this is likely to be a Chinese writer, as bad Chinese transliterations can often change the vowels of an English word, in this case from "Robert" to "Rabert", and native Chinese speakers have difficulty with using the particle "the".