As recently as last month, Republican presidential hopeful Rick Perry (R) was sticking to his 10th Amendment guns, taking a “federalist” line on marriage and abortion rights: what the states want to do is up to them. Then, suddenly, the Texas governor discovered he no longer cared for his own principles, and endorsed constitutional amendments that would ensure states can’t make these decisions on their own.

It was the first of several related moves Perry is making, as his beliefs “evolve” to reflect his national campaign.

For years, Gov. Rick Perry has taken flak for his 2007 attempt to require girls to be vaccinated against the human papillomavirus, the most commonly sexually transmitted disease and the principal cause of cervical cancer. At the risk of angering fellow conservatives, Perry has always insisted he did the right thing.

That unapologetic approach changed this weekend.

A few hours after unveiling his campaign for president, Perry began walking back from one of the most controversial decisions of his more-than-10-year reign as Texas governor. Speaking to voters at a backyard party in New Hampshire, Perry said he was ill-informed when he issued his executive order, in February 2007, mandating the HPV vaccine for all girls entering sixth grade, unless their parents completed a conscientious-objection affidavit form.

The list of admirable positions Perry has taken as governor is quite brief, which makes it that much more discouraging when he reverses course on his best decisions.

Social conservatives have long been opposed to initiatives to combat the human papillomavirus (HPV), which increases a woman’s chances of developing cervical cancer. Merck developed a vaccine that immunizes against HPV infection, and it was approved by the FDA, which led the religious right to fight for restrictions. As the Family Research Council said a while back, the vaccine “could be potentially harmful” to women “because they may see it as a license to engage in premarital sex.”

Let that one roll around in your brain for a moment. A vaccine that prevents deadly diseases is, among some on the right, more harmful because sex is, you know, bad.

Perry, at least in 2007, knew better. Indeed, the governor was refreshingly sensible on the matter: “Providing the HPV vaccine doesn’t promote sexual promiscuity any more than the hepatitis B vaccine promotes drug use,” Perry said at the time. “If the medical community developed a vaccine for lung cancer, would the same critics oppose it, claiming it would encourage smoking?”

That was four years ago. Now he wants to be president, so those principles have been thrown out the window.

It’s genuinely sad to see what becomes of those who run in Republican primaries, isn’t it?

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.