PRESIDENT TRUMP’S nomination of Judge Neil Gorsuch for the Supreme Court elicited an immediate, furious and depressingly predictable reaction. Senate Minority Leader Charles E. Schumer (D-N.Y.) called him an ideologue in a tweet sent a mere half-hour after Mr. Trump made his announcement, and liberal senators such as Sherrod Brown (D-Ohio) and Elizabeth Warren (D-Mass.) announced they would oppose the nomination shortly after that. Conservative activist groups, meanwhile, vowed to go on an election-year-style campaign to advance Mr. Gorsuch’s nomination. The politicization of the judiciary, in other words, continues apace.

We do not blame Democrats for feeling sore about how the GOP Senate last year froze out Judge Merrick Garland, President Barack Obama’s nominee for the seat Mr. Gorsuch would take. Yet many Republicans at least based their opposition on a procedural argument — that the president should not fill Supreme Court seats that come vacant during election years — and refrained from tarring Mr. Garland personally. If Democrats want to retaliate against Republicans for their cynical power play, they should be upfront about that motivation. If they end up voting against Mr. Gorsuch because they think he would rule one way or another on a hot-button issue, such as overturning Roe v. Wade, they should be clear about that, too.

But trashing Mr. Gorsuch as an outlandish radical, despite his impeccable credentials, the wide respect he commands in his field, his long service as an appeals court judge and the unanimous voice vote he received the last time the Senate considered him for the federal bench, is at the very least premature. Democrats should at a minimum give him a chance to appear before the Senate, keeping in mind that the judicial “mainstream” is not composed exclusively of liberals.

The question, then, is what Mr. Gorsuch should be asked about during his confirmation hearings. As with many other Supreme Court nominees before him, the judge will no doubt be loath to discuss specific cases and take stands on issues the court is likely to hear, a defensible position that promotes judicial independence and the appearance of impartiality. Senators should nevertheless demand that Mr. Gorsuch describe his views on when it is appropriate to overturn standing court precedent. A preference for judicial Jacobinism would, indeed, put him outside the mainstream.

Senators should probe Mr. Gorsuch’s “originalist” legal philosophy, asking him what happens when history and legal text do not offer clear guidance. Originalism should not always lead to ideologically conservative outcomes, as some originalists would have it.

They should ask Mr. Gorsuch about handling cases in which general laws conflict with individuals’ religious practices, given his previous rulings on Obamacare’s contraception mandate. They should insist he explain when courts should defer to the executive branch in interpreting the law. He appears to have views that, if acted upon, would significantly expand court power to quash executive actions.

Senators should also ask Mr. Gorsuch about his selection process. Did he make any private commitments to Mr. Trump or his staff? Was he asked to? While on the subject of Mr. Trump, they could ask the judge to articulate his views on libel law, which the president has chillingly proposed to “open up” in order to assail journalists, and they could ask him to discuss what would happen if the president ignored a court order.

The process of filling Antonin Scalia’s Supreme Court seat has already been unreasonable enough. Making it more so would hurt all sides in the long run.