It’s unfortunate that we critique Supreme Court nominees today in ideological or political terms, because the Court is the nonpolitical branch of government. Justices are supposed to apply the law to cases before them — to call balls and strikes impartially, as then-Judge Roberts put it — not decide cases according to liberal, conservative or any other political values. Yet ever since liberals viciously attacked Robert Bork in 1987, that’s the way we’ve judged nominees.

The reason is simple: In large measure, we no longer live under the Constitution. Instead, after turn-of-the-century Progressives came to power during the New Deal, the Court began reading the document not as a limit on government but as a font of endless government powers and programs.

But those programs would eventually have to be adjudicated in the courts, which meant judges would ultimately rule over vast areas of life that the Constitution had left either to the political branches or to private ordering under the common law. And since much of that adjudication would require judges to make not legal but value judgments, it would be important to know just what values they would bring to the court. Thus has politics trumped law, and a Constitution of limited government been turned on its head.

And so we ask now, “What are Elena Kagan’s values?” — although the question will be couched in the more neutral-sounding “What is her conception of the law?” Does she believe, for example, that Congress’ power to regulate interstate commerce — granted mainly to enable Congress to ensure a free national market in light of state impediments then existing — allows Congress to order individuals to buy health insurance from private vendors? Absent that original understanding of the power, which limited its scope, it’s hard to find any limits. Surely the modern reading of the power, that Congress can regulate anything that “affects” interstate commerce, is bounded only by one’s judgment of that amorphous standard — by one’s (value) judgment about what does or does not affect interstate commerce.

Kagan will not and should not answer that question, of course, because with more than a score of states now suing the government over ObamaCare, the question will soon be before the Court. Nevertheless senators on the Judiciary Committee should press her more generally on the commerce power through which the modern regulatory state has arisen, not least because so little is known about her understanding of that and of so much else besides.

Unlike others on the Court, she has never been a judge and so has no body of opinions that might illuminate her understandings. And her record of published opinions is surprisingly thin for someone who hails from the legal academy, due in part, perhaps, to her having served in recent years as a law school dean.

There is, however, a far more basic reason why senators should press Kagan on so fundamental a question as whether there are any longer any limits on government’s power — power, for example, to ban books published by corporations if those books advocate the election of a candidate for federal office 60 days before an election, a position she recently took as solicitor general. (In fairness, her role required her to defend the appalling McCain-Feingold statute, but we still need to know her own views on the matter.) The reason for so fundamental an inquiry is twofold, at least.

First, for better or worse, modern Supreme Court confirmation hearings afford Americans an opportunity to reflect on issues that today are too rarely before the public, especially constitutional issues. Indeed, rarely do members of Congress even ask whether they have the authority, under the Constitution, to undertake proposals before them; they seem to think they may do whatever they imagine is politically expedient.

Second, thanks to the sheer ambition of the Obama administration, together with national indebtedness as far as the eye can see, we have before us today something called the Tea Party movement, the political implications of which have been seen recently in Virginia, New Jersey, Massachusetts and, just this past weekend, in Utah. And what, above all else, is this growing movement saying? “Give us back our Constitution!”

However unsophisticated their understanding of the Constitution may be — by Harvard Law standards — these folks know intuitively that something is fundamentally wrong in the land, and it has to do with our having strayed from our Constitution of limited government. Members of the Senate Judiciary Committee, especially Republicans, will ignore this movement at their peril. Let the hearings begin. But let them be real.