The recent national elections in Britain proved quite a surprise to pollsters and pundits alike. Many had predicted a Labour Party victory under the leadership of Ed Miliband. “Red Ed” had stunned the political world in Britain and beyond by taking on his older brother, David, for the leadership of the party -- and winning it outright. David had been more high profile. As Foreign Secretary in the Labour Government of Prime Minister Gordon Brown, David Miliband had held one of the posts political scientists traditionally see as stepping stones to Number 10 Downing Street. But David Miliband never got the chance to enter the prime minister’s residence in his own right -- at least not yet.

Little Brother Ed based his challenge on an appeal to Labour’s traditional power base -- the Left-leaning labor unions and their ideological partners, the Marxist intelligentsia in the academy and especially in the media. The Miliband brothers’ late father, Ralph Miliband, was one of Britain’s leading Marxist intellectuals. Ralph Miliband had just barely escaped Hitler’s juggernaut 75 years ago. He was doubly marked -- as a Jew and as a Marxist.

Not since Cain and Abel, or more recently, the American Civil War, have brothers so dramatically clashed. Yet, there are lessons here for us on “our side of the pond.” Ed Miliband in the later days of the campaign was touted as having some “weird” wonky appeal to Britain’s restive youth. Some even saw his uncharismatic speaking style, his nasal twang, and his déclassé accent as part of a new image of Socialist Britain.

We’re reminded of Clement Atlee, the Labour Party’s giant-killer who trounced Winston Churchill in 1945. As prime minister, Atlee led a huge House of Commons majority that ended the British Empire and nationalized almost everything (including, notably for us, health care). Hearing the bald, pipe-smoking, mustachioed Atlee deliver a speech was about as exciting as a reading of the Times’ obituary page on New Year’s Eve. Churchill had once dismissed Atlee: he is a modest man with much to be modest about.

Modest or not, neither Churchill nor the redoubtable Margaret Thatcher dared to dismantle Atlee’s National Health Service (NHS) when they entered No. 10 Downing Street in their own right. The tenacity of the Left’s defense of socialized medicine illustrates how hard it is to get rid of once it is jammed through. This is why almost all of the GOP presidential contenders emphasize repeal and replace ObamaCare. And they are wise to do so.

The Miliband v. Miliband clash in Britain is a more dramatic version of a phenomenon we have seen here. Listening to Walter Mondale was about as exciting as watching paint dry. Knowing this, “Fritz” Mondale chose Rep. Geraldine Ferraro as the first woman on a national party ticket. This pair was said to be like the famous dance team of Fred Astaire and Ginger Rogers: He gave her class and she gave him sex appeal.

Mondale also had to move far, far left in order to gain traction. He endorsed abortion on demand, agreed to every demand of the homosexual lobby, and attacked Ronald Reagan’s unapologetic outreach to Catholics and Evangelicals.

Mondale also promised voters he would raise their taxes. The chattering classes loved it. The voters in 49 states didn’t. Like Ed Miliband, the uncharismatic Mondale went down in flames, red flames.

We are seeing a repetition of this today. Hillary Clinton and Elizabeth Warren are not sisters -- except in the sense that they are politically powerful feminists. Yet, Sen. Elizabeth Warren (D-Mass.) is the one the Left-wing grassroots yearns for. And Hillary -- who opposed granting marriage rights to same-sex partners throughout the nation just a year ago -- has thrown marriage off the sled. On immigration, she is trying to move to the left of President Obama.

Hillary is the Clinton with the fingernails on the blackboard speaking style and the tendency to put her foot in her mouth. “Slick Willie” was famous for his ability to wriggle out of tight spots. She is now against his foreign policy, his economic policy, and his domestic policy.

President Clinton signed the ban on homosexuals serving in the military. She now opposes that. Our colleague at Family Research Council, Peter Sprigg, has called that idea “a radical deviation from the unbroken practice of the American military.” Bill Clinton said he was for marriage. He signed the Defense of Marriage Act. She’s against it. He signed Welfare Reform. She’s against it. (All of these issues were ones favored by Family Research Council.) Bill pushed for trade pacts. Hillary’s against them.

In order to pump up her sagging public appeal -- and especially to energize the Left-wing base of her own party -- Madam Secretary is prepared to do anything. If she has to, she will run for the White House against her husband’s legacy.

Ed Miliband also opposed his brother David’s ties to “New Labour.” This was the more centrist approach of Tony Blair. Ed soared in the contest for the leadership, but he crashed on landing.

With as yet no serious opposition for the nomination, Hillary is nonetheless lurching to the Left “The Clintons have no shame,” said George Stephanopoulos famously, “and that’s a great advantage in politics.” Indeed it is. Labourites in Britain could appeal to David to come home. But if Hillary fails, we’ll have to wait for Chelsea.

Mr. Blackwell and Mr. Morrison are senior Fellows at the Family Research Council in Washington, D.C.