Somewhat incorrect, Trump is angry with nato bc they do not contribute what they should to their military. The USA is essentially just giving subsidies to those nations that refuse to pay their share. Its a waste of tax dollars.
Trump's anger with NATO allies' refusal to join the war against Iran and their relatively lower military spending are two separate issues.
@3db is not "somewhat incorrect", he is
absolutely correct. When it became clear that the war against Iran was not going as well as he had hoped, Trump called for the rest of NATO to join in. When we all refused, it was "Fine, we don't need your help". Now that there is still little progress, he is just getting angrier.
He did not consult NATO allies before attacking. It's just as well, because he would have been told, "This is a stupid idea". As the old expression goes, "A lack of planning on your part, does not constitute an emergency on my part". It has turned into a $hit sandwich and now he wants others to take a bite. Why would they do that? We all know what would happen. When the war goes no better with the rest of NATO's help (because it won't), he'll use it as an excuse to blame them for the lack of success.
He did
nothing during his first term to foster good relations with close allies and trading partners and, a year into his second term, he has done nothing but do his best to turn his allies against him - trade wars, lectures from him and Vance to Europeans about
their poor governance (laughable), calling Canada the 51st state and our Prime Minister "Governor", threatening to take Greenland...I could go on, but I shouldn't need to. The point is, he did nothing in advance that would make US allies willing to go the extra mile for him, because we all know it would not be the least bit appreciated*. Also, the fact that this attack on Iran is against international law cannot be forgotten.
*The only time Article 5 of the NATO treaty was invoked, was by the US, because of the 9/11 attacks, to justify the invasion of Afghanistan. Even though that country's relationship with 9/11 was only tenuous, NATO stepped up. Then, when the US invaded Iraq on the flimsiest of excuses, many countries stepped up again. Partner countries spent billions and lost a lot of lives in those campaigns, but Trump insists that NATO never does anything for the US and continues to denigrate their sacrifices.
As for the lack of defence spending by NATO countries, that was most certainly an issue in the past. However, that is rapidly changing. Canada just reached the 2% of GDP threshold and plans to get to 5% by 2035. European allies are ramping up in a similar fashion. As for complaints that the US is "subsidising" NATO, that's nonsense. Nobody is twisting the US government's arm behind its back to get them to spend any more than it wants to. A major factor in US historic assurances that NATO countries would be protected by the American nuclear umbrella was to avoid wide scale proliferation of nuclear weapons. Charles de Gaulle put no faith into this assurance, which is why France developed her own nuclear deterrent force.
If the you don't want to "waste tax dollars", don't just b!tch about it, cut your defence budget.