WASHINGTON -- Republican Sen. John McCain came to an unusual and impassioned defense of Huma Abedin, a top aide to Secretary of State Hillary Rodham Clinton, saying the “sinister accusations” by congressional conservatives about her alleged connection to the Muslim Brotherhood must end.

The attacks have been led by Rep. Michele Bachmann (R-Minn.), the chairwoman of the tea party caucus in the House, and four other conservative lawmakers, who have asked federal officials to investigate whether Abedin, a Muslim American who is deputy chief of staff at the State Department, is using her influence on U.S. policy toward the Islamic group. The lawmakers cite a report showing that Abedin’s relatives, including her deceased father, have alleged connections to the Muslim Brotherhood.

“These attacks on Huma have no logic, no basis, and no merit. And they need to stop now,” said McCain, the GOP’s former presidential nominee and its top voice on defense policy. “I have every confidence in Huma’s loyalty to our country, and everyone else should as well. All Americans owe Huma a debt of gratitude for her many years of superior public service. I hope these ugly and unfortunate attacks on her can be immediately brought to an end and put behind us before any further damage is done to a woman, an American, of genuine patriotism and love of country.”

McCain acknowledged the unusual nature of his decision to come to the Senate floor to speak about a particular individual. But he said he was compelled to do so to protect her character and reputation in the face of attacks being made “without concern for fact or fairness.”

“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,” said McCain, who said he has seen Abedin in action overseas, at Clinton’s side. “I am proud to know Huma, and to call her my friend.”

Bachmann and the other lawmakers have singled out various individuals for scrutiny in a series of letters late last week to the inspectors general at several departments, including State, Defense and Homeland Security. They are seeking investigations into these alleged ties of these individuals, who work for or advise the agencies, to the Muslim Brotherhood.

“We seek answers through these letters because we will not tolerate this group and its affiliates holding positions of power in our government or influencing our nation’s leaders,” Bachmann said in the letter signed by Rep. Louis Gohmert (R-Texas), Rep. Trent Franks (R-Ariz.), Tom Rooney (R-Fla.) and Rep. Lynn Westmoreland (R-Ga.)

The Muslim Brotherhood recently won the presidential election in Egypt, besting the military-backed candidate in the aftermath of the Arab Spring, and Clinton met with President Mohamed Morsi last week in Cairo.

Abedin has long been a quiet presence with Clinton -- on her Senate staff and later on the campaign trail as the former first lady ran for the Democratic nomination for president. She became more known to Americans after Bill Clinton presided at her wedding to former Rep. Anthony Weiner (D-N.Y.), who resigned in 2011, after it was disclosed he sent sexually suggestive text messages to several women who connected with him on social networking sites. Abedin gave birth to the couple’s first child, a son, later that year.

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Lisa.mascaro@latimes.com

Twitter: @LisaMascaroinDC