Interior Secretary Ryan Zinke will leave the Trump administration at the end of the year amid a swirl of federal investigations into his travel, political activity and potential conflicts of interest.

President Donald Trump announced the secretary’s impending departure on Twitter, without providing a rationale, following a Bloomberg News report that Zinke planned to announce his coming resignation on Dec. 19. Trump said a new Interior chief will be named next week.

Ryan Zinke
Photographer: Zach Gibson/Bloomberg

Zinke’s move comes as Democrats, who’ve vowed...