President Obama will not begin interviewing possible Supreme Court nominees until next week at the earliest, according to the White House. So what’s going on behind the scenes?

I don’t know for sure, but I can guess: Apart from vetting the leading prospects to flush out any character flaws, ethical issues or tax problems of the kind that have plagued some Obama nominees, the White House is probably devoting lots of attention to ideological vetting.

The goal of this process, which reportedly started long before it was clear that there would be a Supreme Court vacancy to fill, is to forecast insofar as possible how each prospect might rule on the biggest issues likely to come before the court in the next few years.

Like any president, Obama would prefer a nominee likely to uphold his own personal convictions on such issues as presidential war powers, abortion, racial affirmative action, voting rights, gay rights, religion in public life, assisted suicide, campaign finance reform and use of a litigation as a tool of social reform. Indeed, as someone who taught constitutional law, Obama may care more than most presidents about how his nominee will handle the big issues.

Ideological vetting of judicial nominees is a tricky business. A quotation often ascribed to President Lincoln helps explain why. Lincoln wanted to appoint a chief justice who would uphold the Union’s legal tender law, which required people to accept paper money as payment for private debts. "We cannot ask a man what he will do," Lincoln supposedly said, "and, if we should, and he should answer us, we should despise him for it. Therefore we must take a man whose opinions are known."

But these days, many Supreme Court aspirants take pains to avoid making their opinions known. That’s one legacy of President Reagan’s 1987 nomination of conservative judge Robert Bork. His record of outspoken attacks on major Supreme Court precedents made it easy for critics to claim that he would take a wrecking ball to a long list of constitutional rights, and ultimately to defeat him.

With so many leading prospects hiding their views, how is a president to avoid buying a judicial pig in a poke? Why not just ask, or have subordinates ask, the prospects to state their current views on all the big issues? After all, the views of the current nine justices are a matter of public record. Why shouldn’t prospective nominees put their own cards on the table?

The answer is that — as the Lincoln quotation indicates — the nature of any such conversation would compromise the independence and integrity of the judiciary by creating a huge temptation for the would-be justice to say whatever she or he thinks the president wants to hear — even to make implicit promises to rule as the president would prefer. It would be impossible for the president or anyone else to trust the sincerity of any nominee whose responses to vetters’ questions tracked the president’s own views.

So while White House vetters and senators alike often ask nominees to discuss judicial philosophy in a general way, it is seen as taboo for the White House to ask about specific issues. And any nominee who admitted to answering such questions from White House vetters would expose herself not only to attacks but also to demands that she share the questions and answers with the Senate. This, in turn, would make the nominee vulnerable to attacks by various coalitions of opponents.

This helps explain why every White House depends heavily on interviews with prospects’ professional colleagues and friends to learn what they have said about various issues in private conversations, the better to discern how they are likely to rule. I suspect that a lot of this kind of vetting is going on this week.

The presidential need to have some idea how prospects will rule also helps explain why — despite complaints that the court needs more diversity of professional background — all Supreme Court appointments in recent years have gone to federal appeals court judges.

Most such judges reveal enough about their ideological leanings through their opinions, concurrences and dissents to provide a fairly clear picture of where they are likely to fall on the Supreme Court’s ideological spectrum. At the same time, because appeals court judges are obliged to follow Supreme Court precedent, the more careful ones rarely take such bold or imprudent positions as to energize critics.

In any event, no matter how careful the vetting process, there is no guarantee that the eventual nominee will rule as the president wishes. Lincoln, for example, thought that he had taken "a man whose opinions are known" when he named as chief justice his Treasury secretary, Salmon P. Chase, who had helped draft and advocate the legal tender law. But Chase later reversed course.

At least Chase had the decency to wait until five years after Lincoln’s death to strike down his legal tender law. President Truman was very much alive, and upset, when two of the four personal cronies he had put on the court joined the landmark decision striking down his seizure of the steel mills during the Korean War. "Whenever you put a man on the Supreme Court," Truman later complained, "he ceases to be your friend."

It’s a good bet that Obama, who is at some risk of seeing his own war powers hemmed in by the justices, will do a more careful job of ideological vetting than Truman did.

CORRECTION: The original version of this report misstated Obama’s teaching status at the University of Chicago Law School.