None of our 44 presidents has been an only child — without at least half-siblings. Having your brother as president has meant both unforeseen opportunities and unwelcome scrutiny. Who could forget President Jimmy Carter’s brother, Billy, who registered as an agent for the Libyan government and accepted $220,000 from the Libyans?

Mark Shields

Mark Shields

Seeking to capitalize on his First Brother status, he promoted a brew named Billy Beer. Rep. Mo Udall, D-Ariz., told of buying a six-pack, the first sips of which tasted so foul he sent the rest of the can’s contents in a Mason jar to a chemist friend, who analyzed it and reported, “I am sorry to inform you that your horse has diabetes.”

President Richard M. Nixon, whose resignation embarrassed the nation, was himself politically embarrassed as vice president by his younger brother, Donald, who in chasing his own dream of marketing the Nixonburger in a chain of California drive-ins, sought and accepted an unsecured loan (which he did not repay) from a major defense contractor, Howard Hughes, with no previous interest in the fast-food business.

Neil Bush, son of President George Bush, turned in such a shabby performance as a director of Silverado Savings & Loan in Colorado — whose 1991 collapse cost taxpayers $1 billion — that he and other directors agreed to pay $49 million to settle a lawsuit charging them with negligence.

Later with his brother in the White House, Neil Bush admitted to having extramarital sex with attractive women who “simply showed up” at his hotel rooms in Thailand and Hong Kong and “earning” — while confessing to no knowledge of the product or the process — $2 million for consulting for a Shanghai-based semiconductor company partly managed by the son of the former president of China.

Roger Clinton made big money lobbying his brother for presidential pardons. Poor Sam Houston Johnson had a Secret Service agent assigned to keep him from getting drunk and publicly embarrassing President Lyndon B. Johnson.

President Ronald Reagan’s brother, Neil, may have been the model presidential sibling. He never represented any shady clients before the House Ways and Means Committee, or anyplace else. He was refreshing to interview. He genuinely liked his brother. There were no sour tales about “how Mom liked Ronnie best.”

He came to Washington for his brother’s inauguration, enjoyed himself and then went home to his own life in California. Neil Reagan would have made an excellent permanent First Brother.

But last week, the United States may have lost our greatest presidential sibling when the admirably remarkable Eunice Kennedy Shriver died. Her brothers — John, Robert and Edward — made headlines and made history; Eunice made a difference.

Born to advantage, Eunice Shriver made the disadvantaged her cause. Through her iron will (and while pulling every string available to her as the sister of a president), she led Americans with mental disabilities out of the dark shadows of cruel indifference and isolation into the bright sunshine of acceptance and inclusion. Through the Special Olympics, she changed the way the rest of us see those with disabilities and how those with disabilities see themselves. She taught them and taught us that they could compete as students, as athletes and in the workplace.

Her husband of 56 years, Sarge, spoke openly — and without embarrassment — to me about how much he loved her. Her children’s love for her was unmistakable. But take it from me and everybody else whom she ever enlisted in her work: She was formidable and tough as nails. You did not turn her down lightly, believe me.

Eunice Kennedy Shriver, the most exemplary presidential sibling, quite simply changed the way we, human beings, see each other and how we treat each other. We are a more humane people because of her.

— Mark Shields is one of the most widely recognized political commentators in the United States. The former Washington Post editorial columnist appears regularly on CNN, on public television and on radio. Click here to contact him.