It is easy enough for Donald Trump to berate his compliant attorney-general, Pam Bondi, until charges are brought against his political foes. Making those charges stick in federal court is a heavier lift. That’s the lesson from Monday’s ruling invalidating two cases filed against Trump antagonists.

Trump wants prosecutions of former FBI director James B. Comey and New York Attorney-General Letitia James. When the acting US attorney for the Eastern District of Virginia, Erik S. Siebert, didn’t find sufficient evidence to bring cases, Trump forced him out in September. Bondi installed Lindsey Halligan, an inexperienced White House staffer and former insurance lawyer, to replace him as interim US attorney. Halligan promptly secured indictments from grand juries of Comey and James.

Trump holds a grudge against Comey for investigating him and James for prosecuting him. But Judge Cameron McGowan Currie didn’t throw out the cases because of Trump’s vindictive motive or because of the weakness of the evidence. (Comey is charged with lying to Congress and James with mortgage fraud.) The judge simply ruled that Halligan was improperly appointed. That might seem like a technicality, but ensuring that powerful prosecutors are lawfully appointed is an essential check on the executive.

The problem is that neither the Senate nor a federal court approved of Halligan’s appointment to run the US attorney’s office in Alexandria. US attorneys, the top federal prosecutors in their jurisdictions, are supposed to be appointed by the President and confirmed by the Senate. The attorney-general can appoint an “interim” US attorney for 120 days without the Senate’s sign-off. If 120 days pass without a confirmed US attorney, the local federal court can pick one.

Siebert had been interim US attorney while the Senate considered his nomination. After 120 days, the US District Court for the Eastern District of Virginia extended his service in the role. When he resigned, the “interim” period was over. But Bondi tried to appoint Halligan as interim US attorney anyway.

Judge Currie found that the attorney-general did not have that authority. If Bondi could keep appointing new interim US attorneys despite the statute’s time limit, it would “allow the executive to evade the Senate confirmation process indefinitely by stacking successive 120-day appointments”, Currie wrote.

Currie’s decision, if it stands, means that the indictments Halligan obtained against Comey and James are invalid. But don’t expect that to stop the Justice Department from bringing the cases again, perhaps by Halligan acting under a new title. When it became clear that Halligan’s status as US attorney was at risk, Bondi also appointed her as a “special attorney”.

Will those celebrating Judge Currie’s decision reconsider their attacks on Judge Aileen M. Cannon? She ruled last year in Florida that Attorney-General Merrick Garland did not have authority to appoint Jack Smith as special counsel to prosecute Trump. The cases raised related constitutional issues, and Currie cites Cannon’s opinion in her own.

If the Justice Department manages to get new indictments against James and Comey, the legal wrangling will begin again. Both have strong lines of defence still available to them.

Judge Currie’s ruling ought to be a blessing in disguise. Lawfare does not bring down prices. It’s certainly not what voters want from Washington right now. Successfully growing the economy is a better way for Trump to get back at his haters than demanding more political prosecutions.