Look at the code. It uses a 16-YEAR-OUT-OF-DATE Adobe library.
All the functions do is rotate images in a carousel. They aren't even real numbers, that's why you can't copy them. It's fake counters made out of pictures not data. (Not to mention the US treasury has no public API to pull such data from, anyway).
The main code: https://www.usdebtclock.org/GeneratedItems/CSScriptLib.js
NOT TO MENTION, the site runs Google Ads.
This person is making a fortune on traffic while putting out fake information.
The site is run by CHRONO NUMERIC LABS LLC, which is a fake LLC in Michigan that has the same address as 100s of other fake LLCs.
CHRONO NUMERIC LABS LLC https://opencorporates.com/companies/us_mi/801727644
336 W FIRST STREET STE 113, FLINT, MI, 48502 https://www.bizapedia.com/addresses/336-w-first-street-flint-mi-48502.html (Only displaying the top 25 matches out of 250 total matches)
He is not pulling data from anywhere. He created counters over 10 years ago and just let them count up on their own. He is not estimating shit. He is literally a con artist getting rich off of stupid people like you. He is just like Q, telling people things they already know and making them think "some dumb shit about to happen any day now!".