U.S. Rep. Steve King based his prediction on Obama's pledge to pull troops out of Iraq, his Kenyan heritage and his middle name, Hussein.
"The radical Islamists, the al Qaeda ... would be dancing in the streets in greater numbers than they did on Sept. 11 because they would declare victory in this war on terror," King said in an interview Friday with the Daily Reporter in Spencer.
King said his comments were not meant to demean Obama but to warn how an Obama presidency would look to the world.
"His middle name does matter," King said. "It matters because they read a meaning into that."
The Illinois senator, born in Hawaii to a white Kansas woman and a Kenyan man, is a Christian and has said he has little connection to the Islamic religion, though he acknowledges he spent part of his childhood in largely Muslim Indonesia.
In criticizing King, Obama spokesman Tommy Vietor said, "These comments have no place in our politics." He called on John McCain, the apparent Republican nominee, to "repudiate them like he has previous offensive comments from his supporters."
Last month, McCain denounced an introduction from Cincinnati talk-show host Bill Cunningham, who referred to Obama three times as "Barack Hussein Obama."