Looks pretty clear to me:

In chapter I, article II of the United Nations Charter, it states:

All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.

"The U.N Charter was signed in San Francisco in 1945 by the United States along with 50 other countries. Each country is bound by its articles, and the treaty prevails over all other treaties (including 'special' relationships with other nations). In other words, regardless of any hypothetical attack on Israel, the United States is legally bound not to threaten Iran or any other country. This is also enshrined in the constitution. Article IV Clause II states:"

This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding.

I'm all for it - but exactly how does one purge someone from the Democratic Party?

That's the stumbling block. It's been looked into and there seems to be no way.