One way you can identify politicians' sincere convictions is by looking at the things they do even when they know they're unpopular. There are few better examples than the half-century-long quest by Republicans to destroy Medicare.

As we move towards the 2016 presidential election, it's something we're hearing about yet again. Conservatives know the Democrats will attack them for it mercilessly, and they know those attacks are probably going to work — yet Republicans keeps trying. Which is why it's clear that they just can't stand this program.

When Medicare was being debated in the early 1960s, one of its most prominent opponents was a certain future president, who recorded a spoken word album called Ronald Reagan Speaks Out Against Socialized Medicine. In it, he said that if the bill were to pass, "We are going to spend our sunset years telling our children and our children's children what it once was like in America when men were free." He failed in that crusade, and ever since, conservatives have watched in pain as the program became more entrenched and more popular.

That popularity didn't happen by accident. Medicare is popular because it gives seniors something they crave: security. Every American over 65 knows that they can get Medicare, it will be accepted by almost every health care provider, their premiums will be modest, and it won't be taken away. On the policy level, the program is expensive, but that's because providing health care for the elderly is expensive. It's not because the program is inefficient; in fact, Medicare does an excellent job of keeping costs down. Its expenses for overhead (basically everything except health care) are extremely low, somewhere between 1 percent and 5 percent of what it takes in, compared to private insurance costs that can run from 10 percent to 20 percent and, in some cases, even higher. (See here for a good explanation of these figures.)

That's not to say there's nothing about the program that could be improved, because there certainly is. The Affordable Care Act tried to institute some Medicare reforms, including moving away from the fee-for-service model (which encourages doctors and hospitals to do as many procedures as possible) and toward a model that creates incentives for keeping patients healthy. It's still too early to say how great an impact those changes will have. But Medicare is still in most ways the most successful part of the American health insurance system. And if you care about empirical truth, it's impossible to argue that it's a failure because it involves too much government.

But Republicans do argue that, and it's a belief that springs from ideological faith, not facts. In Wednesday's debate, Rand Paul was asked whether Reagan was right about Medicare, and he responded, "The question always is, what works better, the private marketplace or government? And what distributes goods better? It always seems to be the private marketplace does a better job. Is there an area for a safety net? Can you have Medicare or Social Security? Yes. But you ought to acknowledge the government doesn't do a very good job at it." Paul's ambivalence is obvious — he grudgingly acknowledges that you can have a "safety net," including Medicare, even as he says it's terrible. But if that's so, why not get rid of it entirely?

The presidential candidates who have said anything specific about Medicare all want to move in the direction of privatization, which isn't too surprising. After all, they believe that it's impossible for government to do anything better than the private sector, and if you can take a government program and privatize it, that's what you should do. That's also what new Speaker of the House Paul Ryan believes: For years he's been touting a plan to privatize Medicare by essentially turning it into a voucher program. Instead of being an insurer for seniors as it is now, the government would give you a voucher that you could spend to buy yourself private insurance. And if the voucher didn't cover the cost of the insurance you could find? Tough luck.

When you ask Paul Ryan about this, the first thing he'll say is that he wants a slow transition to privatizing Medicare, one that won't affect today's seniors at all, so they don't need to worry. In Wednesday's debate, Marco Rubio made the same argument. "Everyone up here tonight that's talking about reforms, I think and I know for myself I speak to this, we're all talking about reforms for future generations," he said. "Nothing has to change for current beneficiaries. My mother is on Medicare and Social Security. I'm against anything that's bad for my mother."

In other words: Medicare is a disaster, but we would never change it for the people who are on it and love it so much. They don't have to fear the horror of being subject to our plan for Medicare's future. Which is going to be great.

That contradiction is the essence of the Republicans' Medicare problem. It's one of the most successful and beloved social programs America has ever created, and to mess with it is to court political disaster, particularly among seniors who vote at such high rates. And its success is particularly galling, standing as it does as a living rebuke to their fervent belief that there can never be any area in which government might outperform the private sector.

But grant Republicans this: A less ideologically committed group might say, "We don't like this program, but it's too politically dangerous to try to undo it. So we'll just learn to live with it."

Republicans won't give up. They want to undermine Medicare, to privatize it, to try in whatever way they can come up with to hasten the day when it disappears. And no matter how often they fail, they keep trying.