In what has become a disturbing pattern, President-elect Donald Trump has once again usurped the authority of our current president by weighing in on an issue of longstanding U.S. foreign policy, this time by contradicting the current administration's position on Israeli settlement activity.

The building of Israeli settlements on disputed lands, which has long been a major point of contention in the Israel/Palestine peace process, took a major turn last week when the U.S. abstained on a resolution condemning Israeli settlement activity rather than exercising its veto power. The Obama administration has vetoed every similar measure in the past, but sees this resolution as a means of preserving the possibility of a two-state solution.

The non-binding resolution has, nonetheless, provoked a fierce reaction from Israel Prime Minister Benjamin Netanyahu, who has accused the Obama administration of colluding with other nations to propose the resolution.

Netanyahu has further brazenly politicized the matter by claiming that he has direct evidence of collusion, but will only present it to President-elect Donald Trump following his inauguration — an outrageous and disrespectful end-run around our sitting president.

Rather than bide his time and follow the crucial norm that there is only one president at a time, however, Trump decided to weigh in on Twitter several days after the fact:

The display did not go unnoticed by Netanyahu, who tweeted his thanks to Trump, and curiously, to his children as well:

The Obama administration’s move is controversial, to be sure, but the substance of the resolution is in keeping with decades of U.S. foreign policy. If Trump intends to change that policy, he can begin working on that after his inauguration in just a few short weeks. By weighing in now, he is violating both the longstanding tradition of presidents-elect deferring to the sitting president and the principle that the United States speaks with one voice on foreign policy.

This concept is not just some nicety; it is a crucial practical tool for U.S. diplomacy that allows presidents to negotiate with the weight of the government behind him. Usurping the current president is not just abnormal — it is dangerous.

And it is also becoming old hat for Trump, who recently signaled a radical shift in nuclear policy via Twitter, had his operatives try to remove a key American NATO official, and launched a string of provocations at China.

Perhaps most telling is the fact that Trump did not react to the U.N. vote right away, instead weighing in several days later, immediately following a tweet expressing personal pique at President Obama:

Declaring the end of a smooth transition is reckless no matter the provocation, but in this case, the benign nature of that provocation is very much at issue. The remarks that apparently set Trump off were extremely mild, especially in context: In an interview with David Axelrod, Obama defended his vision of an inclusive America by declaring his confidence that he could have won another campaign, running on the same message and on the accomplishments of his two terms in office.

The short snippet about a hypothetical third Obama campaign has been getting a lot of play, and it is that coverage that has stuck in Trump’s craw over the course of several days. And while it might seem insignificant, Trump’s impetuousness with regard to his own ego and the current U.S. president has potentially dangerous practical consequences, as Trump’s fit over Israel policy demonstrates.

The crux here is that Trump is recklessly conducting an unprecedented campaign to undermine a sitting president’s foreign policy, and also that he appears to be doing so in a petulant fit of egotism. Frightening on their own, the combination of those facts, especially in light of the fraught geopolitical situation in which they occurred, is downright terrifying.