Rand Paul is looking to run the most serious presidential campaign ever by a physician, but in the early going his medical degree is proving more of a complication than a benefit.

Just this week, the Kentucky senator’s presumed expertise as a doctor has set him apart from his potential 2016 Republican rivals in two controversial ways — with his declaration that most childhood immunizations should be voluntary, and because of new details about why he’s not certified by the national board in his specialty of ophthalmology.

As the race for the White House intensifies, Paul can expect his professional opinions and experience to be investigated with more regularity and his statements on topics related to medicine and public health given heightened scrutiny.

Just as a governor running for president would be pressed hardest at a GOP debate for opinions about state sovereignty or unfunded mandates, and a general could expect to be the first one queried about the appropriate use of military force, a physician can count on being asked straight away to detail how he’d reduce the government’s role in the regulation of health care.

“We could try freedom for a while,” was the heart of Paul’s answer on Fox News last month when asked how he’d propose to replace the 2010 health care law, suggesting total deregulation of medical insurance and a reliance on charity to offset reductions in Medicaid coverage of the poor.

Already, social conservatives are flummoxed by Paul’s nuanced position on a central aspect of the abortion debate. Since 2012, he’s championed legislation granting legal protections to the unborn from “the moment of fertilization.” But last fall, he declared his support for use of the so-called morning-after pill — angering many anti-abortion activists, who view such emergency contraception as tantamount to abortion.

Paul also is standing out on another medical topic: He’s the most prominent Republican in the country who favors federal decriminalization of marijuana.

Paul is not the only physician potentially seeking the GOP nomination. Ben Carson, a retired pediatric neurosurgeon, is being ardently promoted by some conservative talk show hosts, but if he runs he’ll likely be hobbled by his lack of any prior elective office.

Carson opposes any relaxation of laws against pot, which he views as a gateway drug. And he also disagrees emphatically with Paul on vaccinations, declaring Tuesday “the rights of parents to raise their children as they see fit” are outweighed by the public-safety benefits of mandatory immunization. A widening measles outbreak this winter, in part because of parents refusing to comply with the rules, has brought the issue to the forefront.

Paul said while he believes in the health benefits of vaccinations and his three children had them — albeit on a slower timetable than normally recommended — they shouldn’t be required. “The state doesn’t own your children,” he said Monday on CNBC. “Parents own the children, and it is an issue of freedom and public health.”

On that front, Paul found some common cause with just one other likely GOP presidential candidate, Gov. Chris Christie of New Jersey. The three other senators eyeing the race — Ted Cruz of Texas, Marco Rubio of Florida and Lindsey Graham of South Carolina — all issued statements Tuesday supporting mandatory immunization.

Paul’s medical background also has been highlighted this week, and not in a flattering way, in a story by The Washington Post detailing his refusal to submit to the American Board of Ophthalmology’s requirements for board certification, which he viewed as unfair to younger doctors, and his effort in the 1990s to create a rival organization that would certify him instead.

Being an eye doctor has been an essential element of Paul’s political story since he started his bid for the Senate five years ago. His 17 years practicing in Bowling Green helped establish him as something other than a libertarian gadfly in the mold of his father, former Rep. Ron Paul of Texas. At the same time, it marked him as just the sort of candidate many conservatives were clamoring for: An outsider ready to give up a lucrative career to crusade against the heavy hand of the federal government on his livelihood — and in an industry, health care, at the center of the GOP’s antipathy toward President Barack Obama.

In that sense, Paul is emblematic of a significant change in the membership of Congress. This year there are 18 physicians and three dentists, more than twice the number of doctors as a decade ago. And there was just a pair in 1992, when Bill Clinton won the presidency on a campaign to remake the health care system. The surge in medical spending, and the sustained intensity of health care as a topic on the Hill, has prompted more and more doctors to run. (Paul is among three GOP physician senators. The House has 15 medical professionals who are Republicans and just three who are Democrats.)

Health care has not been one of Paul’s rhetorical or legislative priorities as a senator, though he made a publicized trip to Guatemala last summer to offer free eye exams, and this year he’s been given his first chairmanship — of the Health, Education, Labor and Pensions Subcommittee on Children and Families.

But Paul’s leveraging of his medical credential is nothing like that of the most prominent GOP doctor ever in Congress — and that’s potentially to his benefit.

Former Senate Majority Leader Bill Frist of Tennessee, a transplant surgeon, gained renown by saving three lives on the Hill between 1995 and 2001. But his own presidential aspirations were dashed partly by his own aggressive application of his medical expertise a decade ago.

After reading court affidavits and viewing a videotape of Terri Schiavo, a severely brain-damaged Florida woman, Frist took to the Senate floor to contradict the diagnosis of doctors who viewed her case as hopeless, then engineered enactment of a law sending her right-to-die dispute to federal court. Conservative groups praised him, but the ridicule he received from his fellow doctors haunted the rest of his career. His planned run for the 2008 GOP nomination never got off the ground.

Correction, 8:30 a.m.

A previous version of this story misspelled Lindsey Graham’s name.

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