Former President Donald J. Trump and his Republican allies have sought to delegitimize criminal investigations into his actions by declaring that Democrats have “weaponized” the justice system. That claim only intensified after a jury convicted Mr. Trump last month of 34 felonies in a hush-money case.

In pushing that narrative, they have tended to ignore an awkward fact: President Biden has not stopped the Justice Department’s inquiry into his own son. On Tuesday, the contradiction sharpened when a jury convicted Hunter Biden of three felony counts for lying about his drug use when he bought a gun in 2018.

The verdict did not satisfy Republicans, who minimized the outcome and continued to insist that Democrats have turned the criminal justice system into their partisan tool. But under tremendous political pressure, 12 jurors in both cases appear to have taken their jobs seriously, weighing the evidence and delivering convictions. The system seemed to work more or less as it is supposed to.

To be sure, there is an argument to be made that both Mr. Trump’s hush-money case and Hunter Biden’s gun case were affected by politics. Both could be characterized as relatively marginal — despite the abundant evidence supporting the charges — cases that prosecutors might not have bothered to bring had the defendants been nobodies. But it was not in either side’s interest to make that point.

Democrats instead lined up after Hunter Biden’s conviction to show off how much they respect the criminal justice system, often explicitly pointing out that they were not criticizing the case as prosecutorial overreach. Despite Republican denunciations of Mr. Trump’s trial as a corrupt sham, they argued, politically prominent people of both parties who commit crimes get convicted.

“The divide here is stunning, and it’s a great reminder that one political party remains committed to the rule of law, and the other doesn’t — it’s that simple,” Representative Jim McGovern, Democrat of Massachusetts, said during a hearing on Tuesday.