What kind of constitution for a militant democracy?

In The Open Society and its Enemies, Popper exposed the paradox of tolerance: Unlimited tolerance must lead to the disappearance of tolerance. Or in other words: if a society is unlimitedly tolerant, its capacity to tolerate will be reduced or destroyed by the intolerant. The paradox can be overcome if tolerance finds limits: if intolerance is exercised with the intolerant. The paradox of tolerance can easily be applied to other public contexts of deliberation and decision such as democracy. If a democratic practice is unlimitedly tolerant with anti-democrats, they will reduce and destroy it. To overcome the paradox of unlimitedly tolerant democracy, Loewenstein proposed the militant democracy model: an interpretation of democracy that describes it as the most legitimate and effective system of deliberation that can best preserve a series of pre-political goods and values, thus the main inquiry is: What constitution would be appropriate for a militant democracy?