Ryan Zinke’s time in the Trump cabinet is ending, but his legal troubles are likely far from over.

When Mr. Zinke was forced to resign as interior secretary on Saturday, he joined a line of officials who have left the Trump administration under a cloud of ethics inquiries. But the investigations into Mr. Zinke’s actions are likely to continue, according to Delaney Marsco, the ethics counsel at the Campaign Legal Center, a nonpartisan watchdog group. And if those inquiries turn out badly for him, Mr. Zinke still faces the threat of criminal penalties that could hobble his political future.

“It’s not a Get Out of Jail Free card to just quit,” Ms. Marsco said.

The most damaging could be a Justice Department examination of a real estate deal in Montana involving Mr. Zinke’s family and a development group backed by David J. Lesar, the chairman of Halliburton, the giant energy services company.

If the department finds that Mr. Zinke willfully used his official position to influence the deal and benefit himself, he could be prosecuted under a federal conflict of interest law and, if convicted, face a sentence of up to five years in prison and a $50,000 fine for each violation. The attorney general has discretion over whether to bring the charges.