What did Donald Trump do today?

He fired his Attorney General to derail the criminal investigation into himself and his campaign.

At some point today—either just before or shortly after he told reporters that he had no immediate plans to shake up his cabinet—Trump fired Attorney General Jefferson Sessions, and replaced him with Sessions' chief of staff, Matthew Whitaker. 

Normally, Whitaker would immediately recuse himself from oversight of special counsel Robert Mueller's investigation into Trump and his campaign's work with Russia to influence the 2016 election. Whitaker is an outspoken critic of the investigation into Russia's sabotage of the election. He also owes his new job to Trump, the main target of that probe, who rearranged the normal DOJ chain of command to hand-pick Whitaker specifically. And he is a personal friend and political ally of Sam Clovis, the Trump campaign figure who is either a witness to or target of the investigation.

Justice Department regulations explicitly require Whitaker to recuse himself under those circumstances. This would leave the deputy attorney general, Rod Rosenstein—another Trump appointee—in charge of the probe.

Whitaker has not recused himself. 

As a result, he will be in a position to make sure that Mueller's team of prosecutors is never authorized to actually bring charges against Trump-connected targets. Or he might simply eliminate Mueller's budget. Both of these are suggestions that Whitaker himself made prior to being made acting attorney general by Trump.

Why is this a bad thing?

• If using your authority to escape investigation or prosecution isn't abuse of power, then nothing is.

• Using your own governmental authority to shield yourself from prosecution is illegal under the federal obstruction of justice statute. 

• No president is more important than the rule of law.

• There's only one real historical precedent here, and it's not a good one.