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.
He's been inaugurated already in secret, which an incumbent president is allowed to do
Inauguration isn't some magic ritual that grants you power, it depends on confidence. Even if he was inaugurated, if 90% of the country doesn't believe it's legitimate, then it's not legitimate. Not to say that they'd be correct.