I'm sorry but what? SpaceX is private, not public, and regardless the Pentagon has zero power to force any such thing. It's making gobs of money and growing pretty fast (around $12 billion revenue this year, prediction is/was ~$15.5 billion so something like a 30% YoY increase) with most of that from Starlink, then commercial launch and gov launch. It launches more mass to LEO then everyone else on the planet combined by a long shot, for far far less $/kg. And it doesn't seem to be slowing down at all. There would be zero interest on either side in a merger, nor is there any particularly good national security argument for it.
The real plan is the same as it's always been: have a reasonably vibrant set of multiple motivated, competitive commercial launch providers. That'll take years more but is by far the better long term solution, and there are plenty of promising options, like Rocket Lab (their Neutron medium lift rocket is apparently close to maiden flight) and Blue Origin (who finally at last seem to have been shaken up and are actually launching rockets and making engines). Old Space wants out of the launch business, which is why ULA came to be at all.
People are also tossing around "nationalization" as if it's some quick fix too all of a sudden, but nationalization doesn't nullify the 5th Amendment (or 1st). The US government would have to come up with the arguably hundreds of billions of dollars present value of SpaceX, at a time of deep budget cuts, debt worries, and high interest rates. It would also have to win a set of massive lawsuits by an extremely well funded opposition about all aspects of the mess that would drag on for years. And a lot of the value of SpaceX is in its institutional knowledge, culture, key people etc etc. Nationalization could not prevent key people all bailing and destroying much of the capability. This would all be hugely disruptive, at a critical juncture, and a big political mess too. It's concerning how blasé folks can get about expensive, complicated big deal gordian knots.