The sentence states: "We should not vote to put at the top of the military's chain of command an individual whose history of excessive drinking is such that that person would be barred from commanding a missile wing."
The phrase "is such that" is a modifier. It modifies or attributes a description to a noun. In this case, "is such that" is modifying the individual being discussed. An easy way to think about it is that the phrase "is such that" is equivalent to "is to the extent that." So the statement is essentially saying: we should not vote to put at the top of the military's chain of command an individual whose history of excessive drinking is to the extent that that person would be barred from commanding a missile wing.
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