Vivek Murthy seems poised to become the next surgeon general of the United States, but the Boston physician will likely require treatment for lumps and bruises sustained on the Senate floor before he moves into the headquarters of the Public Health Service.

Republicans led by Sen. Rand Paul say President Obama’s choice for the once-obscure position is underqualified, too political, and most of all a threat to Americans’ constitutional right to bear arms. Yet they concede they probably can’t stop Murthy’s confirmation now that Senate Democrats have removed the minority’s ability to filibuster most presidential appointees.

Paul is taking his best shot, threatening a hold on Murthy’s nomination when it comes before the Senate. That could be any day now, after the Health, Education, Labor, and Pensions Committee sends it to the floor Thursday in what is expected to be a close, party-line vote. Democrats have a 12-10 majority on the committee.

“I have serious concerns about Dr. Murthy’s ability to impartially serve as ‘the Nation’s Doctor,’ ” Paul said in a letter to Senate Majority Leader Harry Reid on Tuesday. “The majority of Dr. Murthy’s nonclinical experience is in political advocacy.”

Reid, however, has no obligation to honor Paul’s request to hold the nomination, and Paul conceded that Tuesday evening on Fox News. “We can object, we can vote against him, we can tell the public that we don’t think it’s a good idea to politicize the position of surgeon general,” Paul said on Sean Hannity’s program. “But ultimately, he will have the power to roll over us because right now the Senate operates under the iron-fisted rule of one man, Harry Reid. What he says is what goes.”

Since the White House picked Murthy to lead the Public Health Service Commission Corps last year, GOP lawmakers, former surgeons general, and even some doctors outside the political sphere have questioned the pediatric surgeon’s suitability for the job. At the same time, Democratic lawmakers and some of the most influential health care groups in Washington have endorsed the choice.

The argument against Murthy is twofold: that he has staked out a position on gun restrictions, and that he has less experience in the public-health arena than previous candidates for surgeon general.

On the first issue, detractors point to a tweet on Oct. 16, 2012—the night of the second presidential debate between Obama and Republican nominee Mitt Romney—that denigrates proponents of relaxed gun restrictions. “Tired of politicians playing politics w/ guns, putting lives at risk b/c they’re scared of NRA. Guns are a health care issue. #debatehealth,” Murthy wrote.

“In his efforts to curtail Second Amendment rights, Dr. Murthy has continually referred to guns as a public health issue on par with heart disease and has diminished the role of mental health in gun violence,” Paul wrote in his letter to Reid.

“Historically, the surgeon general of the United States has been a position with the purpose of educating Americans so that they may lead healthier lives, rather than advancing a political agenda,” Paul said. “Dr. Murthy has disqualified himself from being Surgeon General because of his intent to use that position to launch an attack on Americans’ right to own a firearm under the guise of a public-health and safety campaign.”

On the second issue, skeptics say that Murthy, 36, has little experience in public health outside of a nonprofit group that he established in 1995 to advance HIV/AIDS education in India and the United States.

The son of Indian immigrants, Murthy received a bachelor’s degree from Harvard University, a master’s in business administration from the Yale School of Management, and his medical degree from the Yale School of Medicine. In 2008, he cofounded Doctors for Obama, a group that later morphed into Doctors for America, which supported the Affordable Care Act before it became law.

In 2011, Murthy served on the White House Advisory Group on Prevention, Health Promotion, and Integrative and Public Health. He is currently an attending physician and instructor in medicine at Harvard Medical School’s Brigham and Women’s Hospital.

“My concerns are not directed at him specifically,” said Richard Carmona, who served as surgeon general under President Bush from 2002 to 2006. “He seems like he’s got a lot of future potential and has done some nice things in his very short career thus far.”

“That said, his nomination to be surgeon general would make him a three-star admiral, and that idea is offensive to men and women in uniform who have worked for 25 or 30 years to obtain that position by merit,” Carmona said. “When the position of surgeon general is gifted to a political ally, does that person really have the credibility or imprimatur of a rear admiral? Does that not diminish the office?”

Asked if any of his concerns were assuaged by Murthy’s appearance before the Senate Health Committee earlier this month—during which the nominee parried questions about his prior political advocacy and enumerated some of his public-health priorities—Carmona responded, “Most of those hearings, as you know, are orchestrated. People go through a lot of training before they get there.”

A spokesman for Democrats on the panel noted that Paul, who is a committee member, did not attend Murthy’s hearing.

Murthy’s supporters maintain that his apparent lack of experience is an asset, not a liability. “I think that if we are to create a new vision for how we do health in this country, we need young people to be in the forefront,” said Jeff Levi, who served with Murthy on the White House advisory group on public health and is executive director of Trust for America’s Health, a Washington-based nonprofit.

“The traditional role of the surgeon general is to be a bully pulpit and a communicator. Whether you’re 36 or 66, that is critical,” Levi said. “I think he knows how to use a bully pulpit…. He is a reassuring figure who communicates well.”

For the most part, the medical establishment approves of the choice, with Murthy drawing endorsements from juggernauts like the American Cancer Society and the American Academy of Family Physicians. Outside Washington, however, a few ordinary physicians are unconvinced. Bruce L. Davidson, a pulmonary and critical-care physician in Seattle who penned a December 2013 op-ed for USA Today, said that he was not reassured by Murthy’s performance during his confirmation hearing.

“Dr. Murthy indicated that one of his areas of focus would be obesity in America. It’s ironic because, according to a new survey from [the Centers for Disease Control and Prevention], childhood obesity has dropped dramatically. Saying that was like serving apple pie. It’s a good fight for everybody to get behind, but it is anything but one of the key crises that American health care is facing. I think it reflects inexperience.”

The office of U.S. surgeon general was made famous in the 1980s by C. Everett Koop, who launched a crusade against smoking and pressed the federal government to take action to curtail the mounting AIDS epidemic. With a square jaw and an antediluvian beard, the 6-foot-1 Koop became a celebrity in his own right, a Republican appointee who won plaudits from Democrats for refusing to let “political meddlers in the White House” affect his work as surgeon general.

Murthy would be the first Indian-American to become surgeon general, but he is not the first to be considered. Sanjay Gupta, CNN’s chief medical correspondent, was approached about the position by then-President-elect Obama in January 2009, but he later removed his name from consideration.

If confirmed, Murthy will replace acting Surgeon General Boris Lushniak, who took over for Regina Benjamin when she vacated the post in July.

Through a spokesman, Murthy declined a request for an interview, as is standard procedure for a pending White House nomination.