Vivek Murthy, the president's choice to be the next surgeon general, is running into confirmation trouble because of an adversary that doesn't normally get involved in medical matters: National Rifle Association. The group sent a letter to Senate leaders late last month opposing Murthy's confirmation because he supports extremely strict gun-control measures.

“Mr. Murthy’s not just a gun control supporter, he’s a gun control activist," the group wrote. "And it’s clear that his agenda is to treat a constitutional freedom like a disease.”

The NRA's opposition has been enough to spook a few Senate Democrats and to put Murthy's confirmation in jeopardy.

Murthy otherwise has the bonafides of a surgeon general: He graduated from Harvard and earned both his MD and MBA at Yale. He practices at Boston's Brigham and Women's Hospital, teaches at Harvard Medical School, and is president of Doctors for America, a nonprofit that focuses on healthcare access and has advocated for Obamacare.

One of the NRA's sticking points, though, is that Murthy once tweeted, "Guns are a health care issue.”

It's not immediately clear what Murthy means by that. The NRA claims that guns are used more than 2 million times a year for self-defense (though social scientists think it's closer to 100,000 times.) And it's healthy to want to defend yourself.