Israel has chosen to stay out of the civil war in Syria, presumably on the basis that having two groups of people who hate you killing each other can’t be a bad thing. That approach works as long as the war continues. Now, however, it appears that Hezbollah is going to emerge as a clear winner. Its troops are battle-tested and better armed than ever.
Unlike Hamas, which is a flea bite, Hezbollah is a serious military threat, and it is backed by Iranian missiles. The only thing that would make matters worse would be an Iranian nuclear capability; that was eliminated by the deal with Obama.
And so, when the next Lebanese war comes (as it will), Israel will have plenty of reasons to thank the Great Satan Obama for his foresight in making the deal that Netanyahu so openly despised. If Trump chooses to tear up the deal, the war will come sooner rather than later, and it will probably involve us as an active participant.