Among those most vulnerable to being dismissed are Sessions and Deputy Attorney General Rod J. Rosenstein, who is overseeing special counsel Robert S. Mueller III’s Russia investigation after Sessions recused himself. Trump has routinely berated Sessions, whom he faults for the Russia investigation, but he and Rosenstein have forged an improved rapport in recent months.

Allies of Sessions and some in the Justice Department believe the attorney general could be fired in humiliating fashion in the days immediately following Tuesday’s elections. The White House has already begun considering replacements, while Trump aides and confidants have cautioned the president he would face a backlash if he fired either of the top two Justice officials, particularly before the midterms.

Other Cabinet officials — including Defense Secretary Jim Mattis, Interior Secretary Ryan Zinke and Nielsen — also face uncertain futures.

Mattis and Trump have long had “an uncomfortable working relationship,” in the words of one former White House official. The two have clashed on a range of issues, including transgender people serving in the military, the Iran nuclear deal, military exercises with South Korea and conflicts in Afghanistan and Syria. Mattis has made securing military alliances a priority, and he has often found himself assuaging European and Asian allies rattled by Trump’s comments.