If Cliven Bundy says that he does not recognize the US government...?

Because he is your typical 'sovereign citizen' hypocrite.

The problem with the sovereign citizens movement stems from its hypocritical stance that relies upon a flawed understanding of how the social contract works. In their case, rather than wholly obeying it a country's social contract, sovereign citizens like to cherry pick parts of it they want to follow and which parts they don't all the while arguing all the time that they're exempt from obeying government.

Sovereign citizens fail to understand that you don't get to do that. By using documents of common law, such as the United States Constitution, and using any part, or select parts, as a justification for being exempt from being government citizens, they're in fact doing the opposite: they acknowledge the social contract has validity and thus are still government citizens. If their misunderstanding of how social contracts work isn't enough, many sovereign citizens still receive and redeem government checks as well as other forms of federal financial aid. This is further inadvertent admission that they are still citizens of the government and don't truly reject it.

What he has a probelem with is a bunch of brown shirts threatening him and his family.

Cognitive dissonance with a dollop of stupidity.

Another conservative hypocrite.

LOVE your country, hate your government.