It's quite possible that the 5% number is one he pulled out, ad hoc.
So naturally, all of the arguments from some will tend to drift away from the underlying sentiment of "the other countries need to step it up" which is perfectly valid, and will instead fixate on the arbitrary nature of the "5% part".
The reality is, the US has been compensating for other countries paying less on defense spending for quite some time (and that's not just isolated to NATO-related matters).
The entire world would come to a screeching halt in terms of maritime trade/shipping if the US pulled back the Navy tomorrow.
- Freedom of Navigation Operations (FONOPS): The U.S. Navy conducts operations to ensure that vital sea lanes remain open, particularly in contested areas like the South China Sea, the Persian Gulf, and the Strait of Hormuz.
- Presence in Strategic Chokepoints: U.S. naval forces operate in key maritime chokepoints, such as the Suez Canal, Strait of Malacca, and Bab el-Mandeb, deterring piracy and ensuring the free flow of trade.
- Counter-Piracy & Anti-Terrorism: The U.S. Navy leads efforts against piracy, particularly off the Horn of Africa (Somalia) and the Gulf of Guinea.
- Escort Missions & Conflict Deterrence: In times of heightened tensions, the U.S. Navy escorts commercial vessels, as seen during the Tanker Wars in the Persian Gulf.
What that translates to is, the US spends more on military and less on domestic social services, so all of the other countries can do the inverse, and then chastise the US for not providing said social services.
The US could reduce its own military spending by 30%, and then use the leftover cash to fund healthcare, education, etc... and the end result would be something that the rest of the world likely wouldn't be keen on.
