It's not like we are running low on people who have the ability to be our leader (though we are running low on candidates worth being our leader lately).
Once again, this is not a valid argument. It's like saying, it's not like we are running low on white Christian males who have the ability to be our leader, so no one else should qualify. The number of people available is absolutely irrelevant.
That argument is a rather difficult one to make. Why would a natural-born citizen be more likely to maintain national security than, say, someone who became a citizen at the age of one?
The argument that naturalized citizens are somehow less likely to owe allegiance to the United States is, I'm sorry to say, entirely unconvincing.