A White House adviser has resigned in a row about crude remarks he made about Republicans, and over his signing of a controversial 9/11 petition, BBC reported.
Van Jones, President Obama's adviser on green jobs, had issued two public apologies in the past week.
One of the apologies was for signing a petition in 2001, which suggested the Bush administration may have allowed the 9/11 terror attacks to happen.
As he quit, Mr Jones said opponents had "mounted a vicious smear campaign."
The row that has engulfed Van Jones centred on video of a speech he gave before joining the Obama administration, and a petition that questioned whether the Bush administration "may indeed have deliberately allowed 9/11 to happen, perhaps as a pretext for war."
On Friday, President Obama's press secretary failed to give public support to the environmental adviser, saying only that he "continues to work for the administration".
In a media statement, Van Jones said the reason for his resignation was to avoid being a distraction in the Obama administration's efforts to pass healthcare reforms and climate change legislation.
"On the eve of historic fights for health care and clean energy, opponents of reform have mounted a vicious smear campaign against me," he said.
"I cannot in good conscience ask my colleagues to expend precious time and energy defending or explaining my past. We need all hands on deck, fighting for the future," Mr Jones wrote in his resignation letter.
Senior Republicans had been demanding Van Jones stand down, with some stating Congress should investigate his "fitness" for the role.
Republican congressman Mike Pence said: "His extremist views and coarse rhetoric have no place in this administration or the public debate."
Van Jones, a former civil rights activist, has been a prominent figure within the environmental movement, and had worked for the White House Council on Environmental Quality since March.
Reports say he had won praise before joining the Obama administration for his vision of a sustainable green economy, one which the Democrats could embrace.