Six years ago, Rick Perry made embarrassing headlines when he could not remember the name of the federal agency he wanted to scrap.

He listed the Department of Commerce and the Department of Education, but failed to recall the third - the Department of Energy. Soon after the performance at that Republican debate, he dropped out of the race.

Mr Perry is now back as Donald Trump’s nominee to head that very same department. But reports suggest the former Texas governor will have a steep learning curve; when he accepted the job, he did not realise one of his major tasks as Energy Secretary would be overseeing the US’s vast nuclear arsenal.

“If you asked him on that first day he said yes, he would have said, ‘I want to be an advocate for energy,’” Michael McKenna, a Republican energy lobbyist who worked on the Trump transition’s Energy Department team, told the New York Times.

“If you asked him now, he’d say, ‘I’m serious about the challenges facing the nuclear complex.’ It’s been a learning curve.”

Mr Perry’s confirmation process before the Senate started on Thursday. If approved, he will replace Ernest Moniz, who was chairman of the Massachusetts Institute of Technology physics department and directed the linear accelerator at MIT’s Laboratory for Nuclear Science.

Donald Trump's inauguration: What actually happens?

Prior to that, the job was held by Steven Chu, a physicist who won a Nobel Prize.

Mr Perry is likely get pressed on the issue of nuclear security, an area in which he has little experience.

In outgoing cabinet memo, Mr Moiz, wrote: “DOE is fundamentally a science, technology and innovation organisation."

He added: “In 2009, the president set forth goals in Prague to secure vulnerable nuclear material and reduce the nation’s nuclear stockpile while maintaining our nation’s security.”

Mr Perry said he regretted his notorious slip. In a prepared statement before the hearing, he said he also accepted that climate change was real.

“I believe some of it is naturally occurring, but some of it is also caused by man-made activity,” he said. “The question is how do we address it in a thoughtful way that doesn’t compromise economic growth, the affordability of energy or American jobs.”

The Associated Press said that during Mr Perry's record 14-year tenure as governor, Texas maintained its traditional role as a top driller for oil and natural gas, while also emerging as the leading producer of wind power in the United States and a top 10 provider of solar power.