The extent to which the US relies on its courts to settle the most contested questions – segregation, abortion and the rights of individuals against the state – means that Barack Obama’s first Supreme Court nomination marks a defining moment for his presidency.

The political and policy importance of the Supreme Court makes the confirmation process intensely polarising. It has long been mired in the culture wars Mr Obama has pledged to move beyond – a pledge that his choice of Sonia Sotomayor is carefully calibrated to respect.

The nomination of a Latina woman is certain to please those who call for greater diversity on the court, but it would be wrong to see it as classic identity politics. Rather, by picking a woman with immigrant parents who worked her way up society’s ladder – someone strikingly like himself – Mr Obama appeals to the American dream while making that dream a good deal more inclusive.

The nominee is a politically astute choice. Some Republicans will oppose her to please a shrinking political base, but others realise that the GOP must broaden its appeal, particularly to the growing Hispanic electorate. Ms Sotomayor is no radical: almost half of the Republican senators still in office voted to confirm her for the appeals court in 1998. As the putative successor to the moderate Justice David Souter, she will not alter the political chemistry of the court. Thus, the chances of a partisan debate are dimmed.

More strikingly, Mr Obama is forgoing an opportunity afforded him by a near filibuster-proof majority: to force through a candidate who could push the boundaries of legal doctrine and give intellectual leadership to the court’s liberal wing. Instead of a counterweight to the conservative Justice Antonin Scalia, the president opted for what he calls Ms Sotomayor’s “empathy” – her sensitivity to the consequences of court decisions for ordinary people.

That still pits the president against those objecting to “activist judges”. While it is an illusion to call for policy-neutral courts, it would serve neither the court nor the country if Mr Obama’s nominee is suspected of putting his policy agenda above the law. The quality of her legal reasoning must be firmly established.

That is the proper function of the confirmation hearing, where Ms Sotomayor’s performance will be critical. Lawmakers should avoid turning the hearing into a forum for posturing or rummaging through the nominee’s private life. An informed debate is what is required.