If you're a Democrat who's considering a run for the Presidency, there's one thing you should never, ever, do. You can tell any lie and your base will let it slide. You can promote crazy tax schemes, anti-American foreign policy, and you can vow to limit individual liberty. You cannot, however, utter the words "life begins at the moment of conception."
For progressives this is the only unforgivable sin. It's the third rail of left wing politics. In a word, it is unforgivable.
...And it's just what Joe Biden has done.