Both sides are responsible.
With the left constantly attacking the nuclear family, individualism, meritocracy, and equality of opportunity, and calling pro-life organizations domestic terrorists, you can expect backlash from the right. People are ugly. They seek revenge. Both sides add fuel to the fire.
Biden promised to unite the country. He didn't. The left believes in moral relativism and all religions are equal and no absolute truth. They say morality is relative to the beliefs of the individual and what's true for you may not be true for me. This is not only self-contradictory (I'm absolutely sure there's no absolute truth) but leads to an anything goes mentality and makes unity impossible.
Last September also brought a long lasting cutoff low mid month, and there were some similarities.
It’s very common for the first deep trough of the season to arrive around the double digits of September, but it usually passes and leads to “false fall.” But when it cuts off and gets stuck in front of a blocking high that’s when things can get messy.