Why would he not? It's not like he respects institutions such as the Supreme Court. And what repercussions has he ever faced for the destruction of norms and guardrails? If anything, he gains even more support.
Damn whoever used that “may you live in interesting times” curse once to many times.
Total US spending on all defense, not just NATO, is ~$900 billion or ~13-14% of federal spending. NATO has a total annual budget of less than $4 billion and we cover something like 15% of that budget, less than 0.001% of military spending and some infinitesimal portion of overall spend.
> for nothing in return
The US gains incomparable wealth from controlling the global prime currency. Part of the enforcement of this primacy is 750 military bases in 80 countries, giving the US a force projection capability greater than any empire in human history. For the US, NATO is just a just an organizational tool to manage resources among it's allies.
All your tax dollars? How much do you think the US spends on defense without giving anything to NATO? Do you think that’ll somehow decrease if you leave NATO? It just means you’ll have to handle everything yourself. At least currently the US gets to charter about half of all their craft from various European allies.
> if the norms mean giving all of our tax dollars to NATO for nothing in return
We do not give our tax dollars to NATO, at least not in any meaningful way. NATO's entire budget as an organization is about $4B/year, which includes valuable shared command/control systems. For the most part, we fund the American military, and we commit to using it in concert with our allies in certain scenarios.
In exchange, we get incredibly valuable hard and soft power. We get access to land in Europe to use as bases, which are staging areas for potential worldwide threats (e.g., an imperialist Russia). We get shared intelligence. We get goodwill with the rest of the West, so that they'll join our trade pacts. We get commitments of Polish tanks and British spies and French manpower if there ever to be a hot war, so that the US can focus on what it does best (air and naval superiority).
But also, you're the only one who brought up NATO. There are myriad unrelated norms that Trump broke the first time around, and will certainly break further this time, that make the institution of "the American government" less able to serve its purpose. Norms like, a president can't pardon himself. A president can't use his position to direct foreign powers to patronize his own businesses. A president can't summon a violent mob to Washington to overturn an election. A president can't conspire with state legislatures and militias to disregard the results of their states' elections. A non-sitting president can't steal classified documents, and can't have ongoing secret communications with a foreign power. A president keeps special counsel at arm's reach. A president shouldn't use tax policy to explicitly punish states that don't vote for him.