Kentucky Sen. Rand Paul — a potential GOP presidential candidate — once compared mandatory vaccination to “martial law,” first wading into the vaccination debate in 2009 when he was running for his first term in the Senate.

“The first sort of thing you see with martial law is mandates, and they’re talking about making it mandatory,” said Paul in a 2009 interview, referring to the H1N1 Swine Flu vaccine. “I worry because the first flu vaccine we had in the 1970s, more people died from the vaccine than died from the Swine Flu.”

The comments, in which he stressed personal health care decision-making, were made during an interview with conservative Alex Jones's InfoWars. The comments were reported by The Washington Free Beacon on Tuesday.

A measles outbreak in the United States has sparked a national debate about the ethics of mandatory vaccination. Paul, a physician, first caused a stir Monday when he suggested most vaccines should be voluntary. Critics quickly labeled his remarks irresponsible.

In the 2009 interview, Paul said that he had received the smallpox and polio vaccines as a child and would opt to take receive them again, but added that “you have to use your brain but I think every individual should be allowed to make that choice.”

“The whole problem is not necessarily good versus bad on vaccines, it’s whether it should be mandatory or the individual makes the decision,” he said. “I’m not going to tell people who think it’s a bad idea that they have to take it because everybody should be allowed to make their own healthcare decisions.”

The national debate has dragged potential presidential candidates into the discussion as well. New Jersey Gov. Chris Christie on Monday was forced to walk back comments in which he called for "balance" in mandatory vaccination following an uproar from critics. Louisiana Gov. Bobby Jindal, another possible GOP presidential candidate, on Tuesday struck a forceful tone in calling for parents to vaccinate their children.

"There is a lot of fear mongering out there on this. I think it is irresponsible for leaders to undermine the public's confidence in vaccinations,” said Jindal in a statement. "I worked in health care for a long time. I have no reservations about whether or not it is a good idea and desirable for all children to be vaccinated.”

Dr. Ben Carson, a retired pediatric neurosurgeon and presidential hopeful, also spoke out in favor of vaccinations Tuesday.

"Although I strongly believe in individual rights and the rights of parents to raise their children as they see fit, I also recognize that public health and public safety are extremely important in our society,” Carson told The Hill in a statement.

Texas Sen. Ted Cruz, another possible contender in the crowded GOP field, told POLITICO Tuesday that his two daughters are vaccinated and that he and his wife "would encourage people to do the same.