All the fencing and securing of perimeters isnt to keep Congress locked in it's to make sure leftists don't riot and actually storm the capitol when it turns out Trump will be President.
Why fortify DC so heavily if you are worried about Trump supporters? Shouldnt they be deployed to different state capitals where the right wingers live? DC is 95% democrat.
I don't think Trump will be sworn in on Jan 20. I think FEMA is going to suspend the constitution, and no one will be sworn in. So when the leftists realize that Biden is not going to be sworn in, then they will riot in DC, and that's why the troops are there.