They are not saying they will only vote for someone who can, as President, change abortion. They are saying that they cannot support a person for President who personally is pro-abortion.
It is about the person's moral character, not the powers of the office. They choose to support only pro-life candidates, regardless of the powers of the office they are running for.
Exactly. A divorcee with enstranged children who authorized the sale of weapons to terrorists like Ronald Reagan would be morally unacceptable to such people.