Trump could add fuel to the obstruction of justice fire, though, if he subsequently used Rosenstein’s ouster to intimidate Mueller or attempt to influence the Russia investigation, according to legal experts. There are several ways this could play out. One is that Trump might pressure Rosenstein’s replacement to curtail the Russia investigation. (Solicitor General Noel Francisco is next in line at the Justice Department.) Trump could tell Francisco, for example, to stop Mueller from pursuing any avenue of inquiry that involves Trump’s financial records or other sensitive topics, or he could order him to fire Mueller and either allow the investigation to continue with a replacement (or without a special counsel at all) or shut it down entirely.
If that’s not something Francisco is willing to do, Trump could try another tack: appointing an acting deputy attorney general who would fill the vacancy created by Rosenstein’s removal. But this could spark a legal showdown, since it’s not clear whether this person would actually be in charge of the Russia investigation until being confirmed by the Senate. Trump could theoretically move someone previously confirmed by the Senate into Rosenstein’s position until a permanent replacement could be confirmed, but this would also likely end up in court because the law that allows this intra-agency reshuffling may not apply to people the president has fired.