The Obama administration's nominee for surgeon general says his top priorities will be fighting obesity and helping communities promote healthier living.

Dr. Vivek Murthy, a Harvard Medical School physician, told a Senate committee Tuesday that obesity is the defining public health challenge of our time.

Conservatives questioned if Murthy's main credential is a political one, because he founded a doctors' organization that has advocated for the Affordable Care Act and he has tweeted about .

But Murthy said if he is confirmed as the nation's doctor, he won't use the job as a bully pulpit for gun control. Murthy also said the is an educator who should help find common ground in improving public health.

Senators haven't yet scheduled a vote on Murthy's nomination.