Civil marriage equality is settled law in the sense that it has been affirmed as consistent with the equal protection clause of the Constitution. I agree with Trump - there's no going back. There will likely be clarification along the margins; e.g., in areas where the current laws respecting public accommodations may conflict with religious liberty, but it's hard to ground a right more firmly than in the equal protection clause of the Constitution.
"Settled law" is more properly the ancient legal concept of "stare decisis" - and that's something anyone with a conservative view of the role of the courts in our system ought to embrace. A proper conservative first and foremost applauds a court that interprets the law rather than makes it, that defers to the verdict of the peoples' elected representatives rather than acts as an unelected legislature unto itself. While I concede that the SCOTUS's decision affirming marriage equality was probably premature - the states had been quickly moving on their own to confirm the right - the grounding of the decision in the equal protection clause was sound as a judicial and Constitutional matter. Besides - a gay couple's right to marry under the civil law harms no one, and affects no couple's heterosexual marriage.
As for the abortion issue, a conservative court cognizant of stare decisis will realize that every woman of child bearing age has had the liberty, for her entire adult life, to decide for herself whether to reproduce. Overturning that right would be as disruptive a move by an unelected court as one can imagine. If the abortion right is to be overturned, it should be done by the people, in the manner provided for in the Constitution - by an amendment ratified by two-thirds of the state.
