They control every branch of government at the federal level, enough states to steal any presidential election, the upper echelons of the military, and every major cultural institution.

And the response has been to let the Left continue to delegitimize every single one of those institutions with further infighting, purging, and ideological zealotry which is not held by most Americans.

Let them collapse the institutions while we build anti-parallel institutions within their sphere of influence. Let them rage, let them scream, and even let them fight. They will continue to fail until we entirely replace those institutions or seize them when they become weak enough to take.

If we secede, we can let them collapse and retake their ground afterwards.

No, you wouldn't... because it's never been done. Even when states split into communist and anti-communist. Instead, you'd get a full throated invasion (like literally ever other time). From that point on, you'd get a massive communist state perpetually attempting to rally an insurgency in the non-communist state until that state's authoritarianism leads inevitably to it's collapse by communist infiltration and propaganda.

This has happened multiple times.

You can't defeat communists by giving ground. At this point, the progressives are essentially relying on right-wing defeatism for all territorial gains because their momentum is being blunted by populism. When you push back on that momentum, you'll get a cascade failure.

The solution to Communists is very simple but requires a great deal of courage and moral certitude.

You shoot them.