It has become evident upon reading a number of "petitions" on this very website a great deal of our populace is illiterate or at the very least uneducated.
It's a worrying idea that the same people who vote for who decides the future of our nation, not just the President but Congressmen as well, can barely write a coherent sentence or adhere to basic principles of common sense and rationality.
Therefore it seems necessary that in order to be allowed to vote, one should have to take and pass a simple test that merely demonstrates the taker is capable of basic mental skills. People who don't know what they're voting for shouldn't be able to vote on what they know nothing about.