John Bryson resigned late Wednesday as commerce secretary, less than two weeks after suffering a seizure and hitting two cars in an incident still shrouded in some mystery.

Bryson, who spent only eight months in his Cabinet post, said in a letter to President Obama that new leadership was needed since the seizure he suffered “could be a distraction” during a crucial time for the U.S. economy.

A former energy executive from California and co-founder of the Natural Resources Defense Council, Bryson was recruited last year to Commerce in part so he could serve as an administration liaison to the business community.

But those plans failed to pan out. Bryson rarely appeared at high-profile business events or as a prominent spokesman in the news media. Administration officials, speaking on the condition of anonymity to talk candidly about the matter, admitted that he wasn’t as effective an advocate as they had initially hoped.

Instead, he led the department as it pursued high-profile investigations into Chinese government subsidies that U.S. firms said were artificially driving down the prices of Chinese products being sold in the United States.

In one of the biggest decisions of its kind ever made by the U.S. government, the Commerce Department announced in May that it was imposing anti-dumping tariffs of more than 31 percent on Chinese solar panels, triggering anger from officials in Beijing.

“Prior administrations perhaps emphasized the negotiation of new trade agreements over enforcing those agreements,” said Timothy Brightbill, a lawyer at Wiley Rein representing a group of U.S. solar-panel manufacturers that pressed the government to pursue the tariffs. “I think the Commerce Department under Secretary Bryson has taken strong steps to enforce the agreements that we have with our trading partners.”

Bryson was also tasked with helping fulfill the president’s promise in 2010 to double U.S. exports in five years. The United States has been on track the past two years to achieve the goal, although the economic problems in Europe and China could slow that momentum.

Bryson’s departure comes after he hit two vehicles near his California home, an episode that initially raised concerns that he was under the influence of alcohol or drugs but was later determined to be tied to a seizure. The incident caught Commerce and the White House off-guard, and Bryson announced he would take a medical leave two days after the crashes.

The legal case against Bryson is still unresolved. A spokeswoman for the Los Angeles County District Attorney’s Office, which will decide whether to file charges, said Thursday that police had not yet turned over the results of their investigation into the crashes.

Commerce officials reached Thursday did not deny that Bryson’s health was a factor in his decision, noting that Bryson suffered a “complex partial seizure,” based on initial tests by his neurologists. Such seizures can cause abnormal electrical activity in an isolated part of the brain that would allow a person to continue performing simple tasks, but leave the person unable to complete more complex activities, neurological experts said.

The Commerce officials spoke on the condition of anonymity to talk frankly about the secretary’s decision to step down.

Deputy Secretary Rebecca M. Blank has been running the department on an interim basis since last week. As part of her new duties, she visited Poland this week for a business summit.

Asked if Obama would nominate a replacement for confirmation in an election year, White House press secretary Jay Carney said only that Obama has “a lot of confidence” in Blank. “Dr. Blank has served in this position already and done it well,” Carney said.

Bryson was the newest member of the Obama Cabinet and served the shortest tenure, having earned Senate confirmation in October. He succeeded Gary Locke, who had stepped down to serve as U.S. ambassador to China.

Obama said in a statement that he accepted Bryson’s resignation Wednesday night, and thanked him for his service.

“As Secretary, John fought tirelessly for our nation’s businesses and workers, helping to bolster our exports and promote American manufacturing and products at home and abroad,” Obama said.

In a letter sent Thursday morning to Commerce employees, Bryson said he felt “privileged” to lead the department.

“In my personal capacity, I will continue to do everything I can to support the President and America’s businesses as they continue to advance innovation, U.S. competitiveness, and prosperity for our people,” Bryson said. “Thank you for your many thoughtful and kind notes over this last week. It has been an honor and a pleasure to serve with you.”

Senate Majority Leader Harry M. Reid (D-Nev.) called Bryson’s resignation “unfortunate,” noting that the secretary was “so anxious” to lead the department last year before finally being confirmed.

As for whether Obama should nominate a permanent successor, Reid said, “I would hope that the president would get a consensus nominee” so that the Senate could move quickly to confirm the pick.

Gary Hufbauer, a senior fellow at the Peterson Institute for International Economics, said the commerce secretary’s role has evolved over time, although the job is limited in its power and can be bogged down by the sheer amount of bureaucracy at Commerce, which also encompasses the U.S. Census Bureau.

“Now the focus seems to [be] more of what can we do to pull up the industrial socks of America, plus what can we do to be . . . more of an export powerhouse,” said Hufbauer. But, he added, the secretary “doesn’t have a lot of levers to do that.”

Staff writers David A. Fahrenthold and David Nakamura contributed to this report.