Accusing Barack Obama of being a Muslim is just about stating that a Muslim is not a capable leader. This is a common prejudice in the United States, where there has not been a single non-male, non-Christian president. There are few political leaders who are not Christian in the US.
Antonio Sabato Jr accused Barack Obama of being a Muslim. He did not accuse Muslims of being bad leaders. More in line he was inferring that Obama is a Muslim extremist sympathizer which makes him a very deadly person in a very large role in the world. The world does not need four more years of Muslim extremist sympathy.
In this day when terrorist acts are occurring frequently both here and in Europe, and when those attacks have all been linked to individuals with radical Islamic beliefs, many have argued that the President is "soft" on the issue of Islamic terrorism. They point out that he is lenient in allowing mass immigration from Islamic countries and his critics also point out that he is reluctant to even say that the criminals in these attacks are "radical Islamic extremists," in spite of their own statements that they are. It is not necessarily out of line to wonder if he is "soft" on this issue due to his own personal beliefs, and such a question does not in itself impugn all Muslims but is specific to him.
Antonio Sabato Jr. from what I know has not suggested anything based on the fact that a Muslim can rule. This debate question is essentially saying that Barack Obama is Muslim which is a bad assumption and is unknown. Muslims, I think, can lead. Look at Osama Bin Laden. Sadaam Hussain. Two examples of very effective leaders.