Arizona Sen. John McCain (R) offered a personal and passionate defense of top State Department aide Huma Abedin in the face of conservative allegations that she is using her position in "unduly influencing" foreign policy in favor of the Muslim Brotherhood.

McCain called allegations that Abedin has ties through her family to the Muslim Brotherhood "sinister" in a rare speech on the Senate floor taking fellow Republicans to task.

"Rarely do I come to the floor of this institution to discuss particular individuals. But I understand how painful and injurious it is when a person's character, reputation, and patriotism are attacked without concern for fact or fairness," McCain opened.

Minnesota Rep. Michele Bachmann (R), a member of the House Intelligence Committee, led four other Republican lawmakers in writing a letter last month requesting that the State Department investigate whether Abedin, who is Muslim, has any ties through her family to the Muslim Brotherhood, an Islamic political group that found success in recent Egyptian elections.

Jacquelyn Martin / AP

Sen. John McCain, R-Ariz.

Bachmann has expressed concerns about how Abedin, who is married to former New York Rep. Anthony Weiner (D), was able to obtain a security clearance.

McCain condemned these accusations as unsubstantiated.

"These sinister accusations rest solely on a few unspecified and unsubstantiated associations of members of Huma's family, none of which have been shown to harm or threaten the United States in any way," he said. "These attacks on Huma have no logic, no basis, and no merit. And they need to stop now."

McCain called Abedin a "friend" who is an "intelligent, upstanding, hard-working and long servant of our country and our government."

"Put simply, Huma represents what is best about America: the daughter of immigrants, who has risen to the highest levels of our government on the basis of her substantial personal merit and her abiding commitment to the American ideals that she embodies so fully," he added.

McCain picked apart the rationale of Bachmann and her colleagues, who wrote their June letter based on a report "The Muslim Brotherhood in America," produced by the Center for Security Policy.

"The letter alleges that three members of Huma's family are 'connected to Muslim Brotherhood operatives and/or organizations.' Never mind that one of those individuals, Huma's father, passed away two decades ago. The letter and the report offer not one instance of an action, a decision, or a public position that Huma has taken while at the State Department that would lend credence to the charge that she is promoting anti-American activities within our government."

McCain has spent time traveling with Abedin while she served as a personal aide to Hillary Clinton during Clinton's time as a senator from New York.

He ended his floor speech with a strong show of support. "I have every confidence in Huma's loyalty to our country, and everyone else should as well."