I fail to see how anything about twitter has any national security implications.
Idiots following idiots following idiots.
Idiots with militaries behind them (with generals who are too chickenshit/dumb to defy orders) are still deadly.
That means the vast majority of Americans do not use Twitter.
And according to this (https://www.pewresearch.org/internet/2019/04/24/sizing-up-tw...), about 80% of the tweets are made by 10% of the users, and most of them are disproportionately young Democrats.
So Twitter is an echochamber within an echochamber.
Were Biden's or Obama's accounts to be hacked, the only effect it would have would likely be with only the extreme fringe of the party. Most Democrats, and virtually all Republicans, would never see it.
For example, if Trump's account had tweet something akin to "all us borders and ports are closed" it would be expected for all border agents to immediately close ports of entry, as similar happened during the original travel ban.