Energy Secretary Steven Chu, a man who has always sought to be the consummate scientist even in the most political of environments, faces perhaps his toughest test yet of his carefully cultivated persona when he heads to Capitol Hill on Thursday to testify about Solyndra.

And his performance this week could offer some clues as to just how long Chu, a Nobel Prize-winning physicist, will remain outside the lab and inside the Beltway.

SPECIAL REPORT

Solyndra, a solar manufacturer that was given a $535 million loan guarantee and touted by the White House as a model for the clean energy economy, has filed for bankruptcy. E&E examines how it got there and what it means. Click here to read the report.

Even before Chu heads to his showdown with the House Energy and Commerce Committee to testify about the half-billion-dollar loan guarantee that his department gave to Solyndra before the company went belly up, the prospect of Chu's departure from his Cabinet post was raised by the release Friday afternoon of an internal White House email in which a former campaign official for President Obama called for Chu's dismissal earlier this year.

In the emails, former campaign energy adviser Dan Carol asked former chief of staff Peter Rouse to consider shifting Chu into a position better suited to his scientific skills.

"Speaking personally and on no one's behalf noted below, I still strongly believe that Secretary Chu ... should step aside to focus on long term R&D and fix the very-broken DOE federal labs -- serving as a new DOE Chief Scientist or perhaps as the new head of" the White House Office of Science and Technology Policy, Carol wrote in March.

In an earlier email to Rouse, Carol called Chu a "wonderful and brilliant man" but said he lacked important skills that the Energy secretary post requires. He said Chu is not comfortable, for example, meeting with bankers and helping the deployment of energy projects "in the messy last mile of political life outside of the lab and university setting."

The documents were released by the White House on Friday afternoon in its effort to comply with a subpoena issued by the House committee as part of its Solyndra probe.

The emails show Rouse was quick to dismiss Carol's criticism of Chu.

"I'm not that interested in Dan's criticism of Secretary Chu, but what do you think of Dan's general assessment of the need for greater focus on our energy policy agenda," Rouse wrote in forwarding Carol's email to other White House officials.

Administration officials also rushed to back Chu after the documents were released Friday, saying there was never serious consideration given to Carol's recommendation to oust the Energy secretary.

"Secretary Chu has the president's full confidence and we are all proud of his tenure as secretary of Energy," White House spokesman Eric Schultz said.

Still, the emails underscore that there are aspects of the Energy post that Chu continues to struggle with.

Washington is "a very political place and [the Cabinet post] is a very political opportunity and he's not particularly good at the political aspects," said Frank Maisano, an energy specialist at Bracewell & Giuliani. "This whole thing with Solyndra, while not his fault, continues to shine the light on that."

Maisano said he did not know if the Solyndra investigation would become a big enough scandal to take down Chu, but he added, "I wouldn't be surprised if [Chu] chose to go in a new direction at the end of this first term. Even if the president is re-elected, I certainly think he may want to get back to academia."

Daniel Weiss, a fellow with the liberal Center for American Progress said today that it is generally assumed that Chu will remain in the Cabinet "at least" through Obama's first term.

Weiss said that while Solyndra has been a black eye for DOE, there has not been any proof of wrongdoing on the part of the secretary.

"It may be Secretary Chu and others could be faulted about optimism of [Solyndra's] success, but there's nothing to indicate so far that they knowingly did anything wrong or illegal," he said. "They may have made miscalculations about the health of the firm, but there's a lot of indication that the company was withholding important information from the government."

And while this week may be a tough one for Chu, Weiss said an upcoming independent review of the entire DOE loan program portfolio is likely to help put the Solyndra loss in context and show the overall success of the program.

That review, which is being conducted by former top Treasury official Herb Allison, is expected to be complete in a little over a month.

Speculation

If Chu does succumb to Solyndra, or to a desire to get out from under the politics of the secretary post, Obama might have a tough time getting a more political appointee through a nomination hearing amid the hyper-political environment leading up to the 2012 election.

Still, several names continue to be mentioned for the job.

Former Michigan Gov. Jennifer Granholm (D), who now teaches at Chu's alma mater, the University of California, Berkeley, has long been mentioned as a possible pick.

Known as an energy innovator during her eight years as Michigan's chief executive, Granholm earned praise for helping to foster the development of battery production and for helping to guide the automotive industry through some of its toughest challenges. She is already close to Obama, having served on his 2008 transition team. She is also media savvy, charismatic and hails from a politically important Rust Belt state.

Another one-time chief executive whose name continues to be mentioned is former Colorado Gov. Bill Ritter (D), who declined to run for a second term last year to spend more time with his family. He now works as director of the Center for the New Energy Economy at Colorado State University.

There is also Washington Gov. Chris Gregoire (D) who, along with being a leader on energy issues in her work with the Western Governors' Association, also announced over the summer that she will not be running for a third term.

If he wanted someone who has proven he can go toe to toe with Republicans on Capitol Hill, Obama might look to someone like Rep. Ed Markey (D-Mass.), a leader among congressional Democrats on energy issues.

Of course, there is nothing to say that the White House won't again look outside the ranks of elected officials if it had to find a replacement for Chu. John Rowe is chairman and CEO of Exelon Corp., one of the nation's largest electric utilities. In that role Rowe oversees one of the largest fleets of nuclear power plants in the country. Exelon also happens to be based in Obama's hometown of Chicago.

One academic with inside-the-Beltway experience is Dan Reicher, who currently serves as executive director of the Steyer-Taylor Center for Energy Policy and Finance at Stanford University. Reicher served in the Clinton administration as assistant secretary of DOE for energy efficiency and renewable energy and was also a member of Obama's transition team. Before joining Stanford, Reicher worked at Google Inc., where he served as director of climate change and energy initiatives.