Marco Rubio in 2024 isn't a person with agency. He will do whatever Trump tells him to do. I wouldn't read much into his appointment other than Trump surrounding himself with yes men. The only person who would get me nervous is Pompeo. That guy is Christian ISIS in mentality.It'll be interesting to see what Rubo and Waltz's appointment will mean for the US's stance on Russia. They were both staunch advocates for Ukraine previously, but in recent months changed their tune to align more with Trump's sentiments for a negotiated settlement. No doubt a large part of this shift was ass kissing to get jobs in the administration, but unlike the Trump, Vance, Maga wing of the Republican party I don't think they would be okay with abandoning Ukraine to its fate if a negotiated settlement couldn't be worked out. Maybe they do prove to be just classic politicians and along with Trump would follow suit in throwing Ukraine's defence responsibilites onto the lap of the Europeans and just going, "have fun, fellas." But I do see on their part some advocacy for continuing confrontation with Russia, compared to other Republicans who still want to pull a "reverse Nixon."
It's also clear eventhough Trump and the media always markets him as an isolationist that Iran is still in the firing line. Trump himself may not have any immediate plans and Iran would still rather not have a war. But Israel would undoubtedly be emboldened further, they already have carte blanche now to depopulate Gaza and go all out in southern Lebanon, they might do the same and strike even more critical Iranian infrastructure, knowing if it does come to regional war the US will have its back.
And based on all this, we know the country that keeps the US awake at nights is still China, but the direction the US goes for Iran and Russia will determine the extent of their China hawkishness. Or maybe they're insane enough to just fight a three front war and hasten the US's decline.