Two years of full-scale war in Ukraine have reshaped the military alliance called NATO (North Atlantic Treaty Organization): Finland and Sweden have now joined, an unintended consequence, as afar as Vladimir Putin was concerned, of his brutal aggression against Ukraine. It is probably correct to argue that NATO is now more united than it has been since the fall of the USSR in the 1990s. NATO announced this month that two-thirds of the alliance’s members have met the goal of spending 2 percent of their gross domestic product on defense. That is a marked increase from a decade ago. But, at the same time, former President Donald J. Trump, the likely Republican candidate, said this month that he was willing to let Russia “do whatever the hell they want” against NATO allies that do not fulfill their commitments on military spending.