WASHINGTON (AP) — Already setting turnover records, President Donald Trump's White House is bracing for even more staff departures and an increasing struggle to fill vacancies, shadowed by the unrelenting Russia probe, political squabbling and Trump's own low poll numbers.

Entering a grueling year that is sure to bring fresh challenges at home and abroad, Trump faces a brain drain across a wide swath of government functions, threatening to hamstring efforts to enact legislation or conduct even basic operations. Some departures are expected to come from senior ranks — the staff churn that makes...