I understand your concern but there are some things a person in public or running for public office has to be very careful about. His answer to the pro-life/choice should be, 'I will support the law of the land,-the wish of the people of this country, whichever it is.' To do otherwise would be, in essence, to disavow one party or the other. Remember, he will be the president of both parties and, as such, must respect the wishes of all.
As an example, a soldier is required to defend the constitution of the US and show respect and be led by the President, regardless of the political dent of the President. A soldier cannot be allowed to criticize in public his commander in chief, no matter what the soldiers personal preference is.