That is a good proportional reason to vote for the lesser candidate, in this presidential election. The problem with the black and white arguments against Democrats will often eliminate the Republican candidate as well, if there is a better third party. That is why the Catholic Church does not use a non-negotiable list, but rather relies on moral teaching, formation of conscience, and prudence.
Nothing can be more important than abortion. However, there are mitigating factors. For instance, one can consider if a candidate is electable. The perfect candidate can be passed over if he is going to garner less than on percent of the vote. He can be, he doesn’t have to be, as one can also consider the impact on successive elections, which might need to build on each other.
Another factor might be the actual ability to affect any change in abortion law, or whether there might be more, or less effect on the number of actual abortions. One could, for example, consider the saving of lives by reducing abortions to be of more importance than a law that has little impact except symbolism on reducing actual abortions.