First off, I don't think you can compare killing an unborn baby to a 2nd marriage, but that is a different debate.
I don't judge anyone, so if he got a divorce then he did, he isn't catholic, so I couldn't say weather or not he would have gotten an annulment if he was catholic.
What I am saying is, as a catholic, how can you support someone who thinks abortion is ok? You asked a question from a question.
Well I understand that if you think abortion is murder, then it's going to be more of a problem for you than divorce is (even if you don't agree with divorce). But in your earlier post you mentioned that according to Catholicism Jesus disapproves of abortion as if that alone is the reason Catholics should not support abortion being legal.
What I am pointing out is that there are lots of things that Jesus/the Catholic Church thinks are wrong (divorce--or at least remarriage after divorce without an annulment, premarital sex, birth control, etc.), but no one thinks that Catholics have to oppose those things being legal just because they are Catholic.
So what I am saying is, some Catholics can vote for a person who supports abortion being legal just as you can vote for a person who supports divorce or premarital sex or birth control being legal.
Some Catholics just don't accept everything that the church says about every issue (especially birth control, sex, gay rights, and abortion). And even if one does accept that abortion is a sin, they might still think it is not acceptable for the government to make it illegal given that not everyone in the U.S. accepts the Catholic Church's view on abortion; there is reasonable disagreement about the morality of abortion and so people might think it is not acceptable to impose one moral/religious view on everyone (his is essentially Biden's position).
In the case of some of my family members, I think they do find abortion to be seriously morally wrong in most cases, but I think they also believe that making it illegal is not the way to prevent abortion. Abortion still occurred when it was illegal, but it was much less safe for women. So I think they favor making birth control accessible, teaching comprehensive sex-ed, and making sure that women who have unwanted pregnancies have the economic resources to have and raise the baby if they choose to--and that view seems to fit in with the Democratic Party much more than the Republican party.