Does a low writing score cripple your test?

I'm a junior in high school, and I took the ACT last month. I got a 35 composite (34 on reading and english, 35 on math, 36 on science), but a 23 on the essay. I have my heart set on an Ivy League (especially Columbia and Dartmouth), and I was wondering, does a 23 merit retaking the ACT, or should I leave it be and focus on APs and grades?

Since you have a 35 composite score, which is above average for both Columbia and Dartmouth, I wouldn't recommend retaking the test. The essay is a secondary concern, especially because scores have been abnormally low across the board on the new version of the Writing section. Since there have been so many puzzling disparities between students' multiple-choice composite scores and Writing scores on the ACT, colleges won't judge you harshly for that 23. Your regular score, which is considered a more reliable measurement of academic potential, is so high as to make the essay virtually irrelevant.

Also note that Columbia doesn't even require the Writing portion of the ACT, so they're even less likely to place any stock in your essay score. Dartmouth does require it, but again, I don't think they'll be concerned with your lower score considering the fact that you performed so well on the other parts of the test. Set the ACT aside, and focus on excelling in your classes and preparing the rest of your application materials.