Andrew Left, the activist short-seller known for calling out overvalued companies, just did something unusual: He highlighted a stock he thinks the market is completely missing.

The Nuclear Contractor Nobody Knows About

On Wednesday, Left's Citron Research posted on X about Virginia-based Amentum Holdings Inc. (AMTM), a contractor that apparently runs most of America's nuclear infrastructure without much fanfare. According to Citron, Amentum "manages 90% of America's nuclear infrastructure for the DOE"—that's the Department of Energy, for those not fluent in government acronyms.

This isn't some niche consulting gig. The company oversees nuclear weapons operations, handles radioactive waste cleanup, engineers new reactors, and manages defense nuclear facilities. "This isn't a contractor," Citron's post emphasized. "This is the keystone of U.S. nuclear capability."

So why is Left suddenly talking about a nuclear contractor? Because President Donald Trump just made nuclear energy a centerpiece of his energy policy, and Amentum sits right in the middle of it all.

Trump's Nuclear Ambitions

The Trump administration kicked things off with a $1 billion Department of Energy loan to restart Three Mile Island—yes, that Three Mile Island. Then came the big one: a May 2025 executive order mandating 400 gigawatts of nuclear power by 2050. That's four times today's levels, which is an absolutely massive buildout.

The DOE already has a $250 billion loan program set up for the nuclear industry, and according to Citron, Amentum is "the only company with the expertise, clearances, and relationships" to actually execute these projects. That's a pretty compelling moat when you think about it—you can't exactly hire a new contractor to manage nuclear weapons facilities without decades of institutional knowledge and security clearances.

Citron also connected the nuclear push to AI infrastructure, pointing out that AI data centers have voracious energy appetites. Nuclear power is increasingly seen as the only realistic way to provide clean, reliable baseload power for these facilities at scale.

The Valuation Case

Here's where Left gets animated. Amentum trades at 10 times earnings, which Citron called "absurd" given that industry peers trade at nearly double that multiple. The firm argues Amentum has superior margins, multi-decade revenue visibility, and essentially a monopoly position in a sector that's about to boom.

"The market will figure this out," the post concluded. "The only question is when."

Market Response

Investors are starting to catch on. Amentum shares jumped 17.12% on Wednesday alone, closing at $25.52, and tacked on another 1.88% in overnight trading. Year-to-date, the stock is up 17.82% as the nuclear revival narrative gains momentum.

Earlier this year, Trump's nuclear executive orders triggered a broader rally across nuclear-linked stocks, with investors positioning for what could be decades of sustained government spending and private investment in the sector. Amentum, as the primary infrastructure manager for the DOE, stands to benefit from virtually every aspect of this buildout—from new reactor construction to waste management to weapons facility operations.

Whether Citron's valuation call proves prescient remains to be seen, but Left has certainly put a spotlight on a company that was operating well below the market's radar. In an era where AI and energy security dominate headlines, the firm managing America's nuclear backbone might finally be getting its moment.