That the legal argument for the president’s amnesty is weak is understating it. Unlike the previous amnesties he cites as precedent, the president’s Deferred Action for Parental Accountability, or DAPA, is not responding to a particular crisis but is simply the enactment by fiat of his own political wishes. Furthermore, unlike those previous amnesties, the president’s offers positive benefits (e.g., work permits) to millions of Americans in the country illegally. Even the administration admits that the order must be executed on a “case-by-case basis,” but the number of affected individuals — somewhere around 5 million — shows it is simply a new dispensation for an entire class of immigrants. And, of course, for years the president himself maintained that such a sweeping act would be outside his constitutional authority. Ms. Lynch apparently is bothered by none of this.

Some Republicans — notably, Arizona senator Jeff Flake in January, and Jeb Bush this month — have said that a president should have broad latitude to choose his team. But surely that does not require confirming to office a nominee who has publicly promised to flout the duties of that office. That is what Republicans would be doing here with a vote to confirm.

Rejecting Ms. Lynch’s nomination would be a forceful rebuke to the president. But, more importantly, it would be a clear indication that Senate Republicans refuse to be complicit in the president’s lawlessness. Yes, Eric Holder or an acting attorney general would be left in office, but Republicans would at least have demonstrated their unwillingness to aid and abet the executive branch’s usurpation of congressional power.