I doubt Rubio will recover enough to capture the castle, this election year. He's out of his depth and, as far as I can see, is so self-conscious about himself that he feels the need to over-prepare himself and therefore repeatedly rely on script. This is not something he's going to radically improve on in 2-3 months while being in front of the world press and social media, that's a brutal learning curve.
He ticks so many boxes for the Republican party, though, and he's clearly a capable, charming, thoughtful and intelligent politician, I don't think this is his year, 2024 just makes far more sense for him. Time enough to develop the experience, resolve, and political catalogue that he needs, and poised then to win back the White House for the Republicans, finally being able to court the voter bases they've perenially struggled with, after what will feel like 16 long years of tired, centrist Democratism for the American public. The Republican establishment will deal with Hillary Clinton in the White House, they dealt a well enough hand with the last President Clinton, and ride out the next 8 years. If the main point of power for the US presidency is foreign policy, Hawk Hillary is far more in line with a lot of the Republican establishment than some of their own current candidates anyway.
At this point, I'd call it out that if this goes the way The Establishment wants (based purely on the current deal of cards), then the next 8 years of world diplomacy will be Hillary Clinton's to deal with.