Why is abortion the number one issue with all democrats, all the time?
Lets consider the political advantages as well.
(1)they have to mop up the detritus of their half century attack on morality and marriage. Namely babies they cant support..
(2)they believe it neutralizes men politically. Their men are girly-men (liberalism is always feminizing...except for the women who seem masculine) and willing to roll over and cower which means they cant object to any bill, no matter how hideous, when they tag it with an abortion rider.
(3)little bit of mafioso here. Like "making their bones". Anyone partaking of abortion has no room to judge (they fear being judged more than almost anything) and also the person has proven her willingness to ignore morality, decency and natural instincts.
(4) only a liberal is repulsive enough for abortion. So by demanding abortion loyalty they get really really liberal judges and appointed officials.
(And finally (5) it is incredibly lucrative and tends to expand government and benefit the media elites. They started with "i alone will control my own body" and ended with "you will pay for my abortions".
The fund raising is huge as well.