Don't be an idiot.
Now, based on 1 John 2:22:
22: Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son
You may argue that Obama is an antichrist, depending on whether or not you believe that he is genuinely a Christian. But in such a case, the term "antichrist" is ultimately synonymous with "non-Christian," and would hardly give him any distinction.
But in terms of calling Obama "the Antichrist," as in the final world ruler, associated with the "Beast" of Revelation 13 (which can be taken to refer either to a person or to a satanic government system ruled by him), this is simply ridiculous.
There really needs to be an evangelical equivalent to "Godwin's Law."
That is all.