In reality, the only entity that can protect the US economy from other government aggressors is the US government. This has nothing to do with domestic politics. The ex-im bank protects the US economy from trade war with other countries. You are implying that AIG and other insurance companies should be able to protect itself and fight in War with other countries.
The only thing that can protect the US Economy are those that are
productively participating in that economy. To the extent people involved in governing skew the economy for and against particular participants, it damages it.
In "reality" the US government is the greatest enemy of the US economy, and the entity best able to wreck it despite its good intentions.
You're suggestion that the ex-im bank is an instrument of war is not so persuasive in justifying it.
Its like cutting off your arm to use as a weapon, sure it extends your reach for the matter at hand, but afterward you are one-armed and there are more fights ahead. There are better tools to achieve your goal then undue market influence by those subject to political influence. Yes, even AIG is better, its only partially a government agent, apparently on an as-needed basis.
Crypto currency is also among those better tools. Government would be better served getting the hang of what it offers before its left behind.