Re: Monopoly?
The US government may not have much choice in the matter.
Trust in Regulators
There's other problems for Boeing, other than late delivery. The relationship between the FAA and the rest of the world's regulators took a serious knock over the 737 MAX crashes. Whilst the FAA has evidently been working hard to repair that international relationship, Boeing then proceeded to not fix their problems, and then let a door fall off an Alaskan Airlines MAX. Since then, the FAA has been heavily involved in how Boeing is run. The certification flights for the 777X are the kind of thing that are supposed to commence, when everything else has been thoroughly gone over.
However, the thrust links broke, risking engines departing the airframe. Technically, that counts as a "near miss", because these aircraft have flown to and done demo flights at air shows all over the world, all while the engines were not as thoroughly attached to the airframe as they should have been. That's basic stuff, something that should have been worked out and pummelled on the ground, something that should have been done before ever a prototype flew. And this has also happened on the FAA's watch.
FAA Could Lose Its Teeth
And now, Elon Musk is talking about getting the Supreme Court to reign in the FAA and prevent them from fining companies. If he achieves that, the FAA is in effect no long a regulator; they cannot "force" any company to do any thing, as there are no actual sanction they can apply. For example, if the FAA withdrew Boeing's manufacturing certificate, Boeing could say "we're carrying on anyway", and the FAA would have no means of making that choice painful for Boeing to pursue.
Dilemma for Overseas Regulators
So the question overseas regulators are still having to ask themselves is, is the combination of the FAA and Boeing capable of delivering safe aircraft? The answer is most definitely not an unequivocal "yes". That then puts the regulators like EASA, CAA, CAAC, in an awkward and difficult position.
To allow Boeings to continue flying over their territories, the regulator staff themselves are taking a personal risk. The buck really does stop with them, and them alone. If they're accepting FAA certifications when there's clear evidence that Boeings are not up to standard, there's the prospect of a negligence case being brought against them. One way forward is that (for example) the EASA were to insist that Boeing certify their aircraft through the EASA. That would kill Boeing, because suddenly the certification costs of their aircraft would be doubled.
Impact on Boeing's Order Book
So the scene is set for Boeing to lose its international market, if the company / FAA continue to let slip-ups through to flying aircraft. If that were to happen, the majority of Boeing's order book evaporates. And there's no way the US gov could keep the civil part of BCA operating whilst being able to fulfil only US domestic orders.
There's nothing the US gov can do about that. If the EASA says "the game's up" to the FAA, the US gov cannot order, oblige, instruct, coerce or influence the EASA to change their mind. The EASA is a EU commission body, and there is no real diplomatic means to apply pressure to the EASA.
Political Failings
This is all the result of the US politicians of both parties over the decades having denuded the FAA of the necessary resources to be able to keep control of a company run by MBAs who have no inkling that the regulatory compliance is a market expander, not a cost to be minimised. It wouldn't have been a problem had the motivations of the company management been benign, naturally compliant. But, it wasn't.
The warning signs have been there for at least 2 decades, but the politicians didn't listen to advice.
If the US government wants a guarantee that the USA will remain in the airliner designing / manufacturing business, it either needed to have taken control of Boeing about 15, 20 years ago, or it could today ask Airbus to become a global monopoly with a large presence in the USA.
Industry Will Not Wait for Government
Even here the US government has comparatively little influence. The types of company that supply both Boeing and Airbus are already talking to Airbus, and it's no secret that some airlines would order even more Airbuses if there were even the remotest chance of Airbus being able to build them. They're doing this because, at the moment, Boeing aren't ordering anything (whilst the strike is on), and the suppliers are desperate to sell product. Airbus could be driven into being a monopoly by the rest of the market.
In these circumstance, the US gov would have to hope that some of Airbus ended up remaining in Mobile, Alabama.