Republicans and unions are like oil and water: They don’t go together. Except for one big exception. Republican politicians support police unions and unionized fire fighters too, often exempting them from the scorched earth policies they direct toward other public sector unions, like teachers and government workers.

“The police are the domestic version of national defense,” says Sam Popkin, a political science professor at the University of California, San Diego. “The reason that Republicans love them so much,” he explained, it that Republicans “identify very strongly in a time of change and turbulence with the troops that provide order. The police are very popular with Republicans and with the middle class in general.”

When Wisconsin Governor Scott Walker cracked down on collective bargaining rights of public-sector unions, he exempted cops and fire fighters. He feared the police might go on strike and join the protestors. Videos of that pairing could have doomed Walker’s entire effort. “It’s a decision by politicians not to bite off more than they can chew,” explains James Sherk, a labor policy expert with the conservative Heritage Foundation.

More doctrinaire conservatives don’t believe in these exceptions. “For the record, I do not believe unions belong in government—including the police force,” Sherk said in an e-mail. The same arguments Republicans make about individual liberty and choice when it comes to opposing union membership should apply with equal force to the police, he says.

But Republican elected officials tend not to toe the conservative line, in part for political reasons.

“Not only are the police likely to vote Republican but the union is the mechanism to mobilize them,” says Ruy Teixeira, a senior fellow with the liberal Center for American Progress. “It’s about knowing which side your bread is buttered on.”

Ohio Governor John Kasich didn’t carve out a special place for police and fire fighters when he cut the benefits and rights of public service employees. He just won reelection by 31 points, and is talked about as a potential presidential candidate based in large part on the reforms he enacted. Philip Dine, a longtime labor reporter and author of “State of the Unions,” explains that conservatives think public service unions are illegitimate because they give to Democratic candidates for local and state offices, help them get elected, and then bargain with these very same people to get good contracts at the expense of the taxpayers.

Dine details what he calls a “concerted effort on the right, whether it’s motivated by ideology, economics or politics, to destroy public sector unions.” The GOP is driven in part by the fact, that three years ago, public sector union members became the majority of union members. The labor movement was once almost entirely in the private sector, but since the 1950’s, labor’s high point, the growth has been in public sector jobs while private sector union jobs, like manufacturing, left the country.

Today, private sector unionized workers are not even ten percent of the work force. “When you attack public sector unions now, you are attacking the heart of the U.S. labor movement,” says Dine. The Great Recession also provided the perfect environment for politicians to stir up resentment among non-unionized workers about union pensions and benefits that governments could no longer afford, and that taxpayers are underwriting.

It’s not 1968 all over again, when cops were beating up anti-war protestors at the Democratic Convention in Chicago, and Republicans became the law-and-order party. The video showing cops piling on Eric Garner in Staten Island for refusing arrest elicited outrage across ideological lines. Some Republicans, notably Rand Paul, began speaking out against heavy-handed police tactics after Michael Brown’s death at the hands of the police in Ferguson.

Still, Republicans were quick to sympathize with a New York police union official who said Mayor DeBlasio, a Democrat, had thrown cops “under the bus” in saying his teenage son, who is biracial, has reason as a young black man to fear law enforcement.

“He’s the mayor, he has to maintain morale among the police,” says Jack Pitney, a professor of politics at Claremont McKenna College. “On the other hand, a lot of people think that was a miscarriage of justice. And so it’s a tough issue for conservatives, they support the cops and on the other hand, you see that video, it’s hard to defend.”

Like so much in American politics, the debate about cops goes back to Nixon, says Pitney. Prior to the 1960’s, law and order was not a big national issue. In the 1960 campaign between Richard Nixon and John F. Kennedy, there was virtually no discussion of crime. “Eight years later, it was central,” says Pitney. “The rate of violent crime had nearly doubled, so Republicans took ownership of that issue.” From then on, the GOP was the law-and-order, pro-police party, and even though crime rates today are the lowest they’ve been in some time, “the alliance with the police is one legacy of that era, and that’s especially true in New York City,” says Pitney.

Law and order infused political campaigns in the eighties and nineties, notably electing former U.S. attorney Rudy Giuliani mayor in 1993 and elevating his “broken windows” view of crime-fighting that is credited with New York City’s renaissance. But all that may have run its course. Excessive force to combat minor infractions of the law is the central issue today. Through it all, the GOP’s alliance with the police endures for reasons both political and cultural. “It’s really quite simple,” says Ralph Nader, who has spent a lifetime fighting for labor and against what he calls the corporatists. “How many people get called by the Fraternal Order of the Police and say no?”