I see this abstention as a 'two-for'; since Trump, in his ignorance, argued before the vote that it should be vetoed and so excited his 'base' ; Obama had a chance to put Trump in his place by not following his lead for which Trump would have taken credit for setting US policy. Second, Obama supports the rule of law which plainly stated the illegality of the Israeli settlements in territory it seized in 1967 against the original 1949 UN resolution which the US endorsed.