An armed populace practically can't be subjugated by any outright oppressor, be it foreign of domestic. If you have to have a gunfight with, and kill most of the populace, then you didn't really 'win' as an oppressor. You can't kill them all.
First, subjugation has many forms. Can you buy a non-low flush toilet in the U.S (federally mandated by George Bush (first) since 1997) no matter how many guns you own? Can you deposit over $10,000 without being reported to the federal government? Can your land be forcably purchased to build a shopping centre?
Second, "force" can be coersive, not just physical. So you have guns. Do you have money? Not any more you don't. Do you have electricity, water, internet, phone service? Nice while they lasted. Can you leave home and go anywhere to get food, gas, or other supplies? Those were the days. No matter how many guns you might have, a seige will eventually end - and not worth it for most people.
Third, both George W Bush's war in Iraq, and Putin's actions against Ukraine shows that even in a modern internet-connected world, the vast majority of a country's population can be completely convinced of something that is demonstrably not true (Iraq had no weapons of mass destruction, Ukrain wasn't overthrown by Nazis putting Russians into concentration camps). When Iraq invaded Kuwait, the daughter of the Kuwaiti ambassador to the U.S testified to Congress that she was actually a nurse in Kuwait who watched Iraqi soldiers dump babies out of incubators to die on the floor (no such event was ever confirmed) - nobody asked even the very first question that would have exposed this lie. Opponents of the U.S government can be adequately demonized, then taken down with overwhelming public support.
Fourth, acting against the entire population might be impractical, but it's much easier to target specific groups one at a time. A large percentage of the U.S population already has nearly no rights already, as a result of nickle-and-diming laws that build up. For example, some states charge court fees to the accused, even when they are found innocent (i.e you used the court to prove your innocense, you must pay for that service), even for a minor crime like tresspassing. The poor often cannot pay, and can be imprisoned for that. There are prison fees, and failing to pay those can extend the term or result in reincarceration on release. There has built up a population of "un-people" who are otherwise law-abiding, but must avoid arrest, relying on a growing underground society of family, friends, and criminals to get illegal work, handle finances, find places to live, and so on. When sick they can't go to the hostpial or be turned in (they have back room "clinics"), when a victim of crime they can't go to the police. They can't use banks (so need cash, which the police can take as mentioned in the posted story). For other people, many are denied voting rights due to technicalities like lack of a drivers license or permanent residence. People caught urinating in public are put on a sex offenders list, which has such impossible restrictions on where to live and limits to work these days that many need to go into hiding just to survive. Minorities are stopped and searched on New York streets for no reason other than being black or hispanic.
Those are things that are already done. Those laws and actions are supported because the victims are "criminals" and in a black-and-white viewpoint, a "technical criminal" is as much a criminal as a murderer, and deserves no rights (and to be accused is to be a criminal).
All put together, this means even if the entire free population of the U.S were armed and trained, they could still be subjugated completely by a government that wanted to. Keep in mind that the repressed population of Iraq (pre-2003 overthrow) was also heavily armed (rifles mostly), but that didn't help them against Saddam Hussein's well organized repression.