When President Obama taps Solicitor General Elena Kagan as his nominee to replace retiring Supreme Court Justice John Paul Stevens this morning, he will be will making a cautious choice that runs the risk, in the words for former National Lawyers Guild president  Marjorie Cohn "move the delicately balanced court to the Right."

Attorney General Eric Holder may believe that Kagan will "be a great justice."

And there is no particular reason to argue with the assessment from People For the American Way President Michael B. Keegan, who said Monday that: “Elena Kagan is a bright and clearly qualified nominee."

But Keegan stopped short of a full embrace of the pick.

"I look forward to the confirmation process and learning more about the judicial philosophy she’ll bring to the high court," the head of the liberal watchdog group, which has a long and admirable record of monitoring court picks. “This confirmation process presents a unique opportunity for a dialogue about the role of the Court and the meaning of our Constitution.  Over recent years, the Roberts Court has pushed a political agenda from the bench, favoring corporations and powerful interests over the rights of ordinary people.  We’ve seen longstanding Constitutional principles and laws designed to protect families and individuals casually tossed aside in pursuit of a rigidly conservative ideology.

Keegan says he looks forward to a "national conversation" about the Kagan nomination, and so should we all.

That conversation should begin with an honest admission that Kagan’s record does not suggest that she will be as great, or as liberal, as Stevens.

Cohn, a Thomas Jefferson School of Law professor, has raised alarm bells with regard to Kagan.

"The founders wrote checks and balances into the Constitution so that no one branch would become too powerful. But during his "war on terror," President George W. Bush claimed nearly unbridled executive power to hold non-citizens indefinitely without an opportunity to challenge their detention and to deny them due process. Three times, a closely divided Supreme Court put on the brakes. Justice Stevens played a critical role in each of those decisions. He wrote the opinions in Rasul v. Bush and Hamdan v. Rumsfeld and his fingerprints were all over Boumediene v. Bush," she explained on the eve of the nomination.

"Unfortunately, President Barack Obama has continued to assert many of Bush’s executive policies in his ‘war on terror,’" adds Cohn. "Elena Kagan, reportedly Obama’s choice to replace Justice Stevens, has never been a judge. But she has been a loyal foot soldier in Obama’s fight against terrorism and there is little reason to believe that she will not continue to do so."Of particular concern to Cohn was that fact that, during her confirmation hearing for solicitor general, Kagan agreed with Senator Lindsey Graham that the president can hold suspected terrorists indefinitely during wartime, and that the once narrow scope of "battlefield law" could be expaned to apply globally in a "war on terror" moment.

So what’s Kagan’s appeal?

Why is she being nominated now?

Some might argue, cynically or not, that Obama is all about expanding executive power.

But it’s not really that.

Kagan is an easy pick.

As a Judiciary Committee member told me over the weekend, White House aides were especially interested in Kagan because she has already been confirmed by the current Senate. When Obama nominated the first female dean of Harvard Law School, to serve as Solicitor General, she was easily approved on a 61-31 vote. Despite some conservative criticism of Kagan for raising concerns about the Bush-Cheney White House and Judiciary Department misinterpreting of "battlefield law" in a manner that would apply it off traditional battlefields—as a justification for the previous administration’s indefinite-detention policies—the nominee earned the support of key Republican senators, including a pair of Judiciary Committee stalwarts, Utah’s Orrin Hatch and Arizona’s Jon Kyl; conservative firebrand Tom Coburn of Oklahoma; and moderate Mainers Susan Collins and Olympia Snowe.

On Capitol Hill, Kagan is seen as a cautious choice rather than a liberal champion. Veteran court-watcher Jeffrey Toobin, describes the Solicitor General in pretty much the way that Democratic members of Congress I’ve spoken to see her: as "very much an Obama type person, a moderate Democrat, a consensus builder…"

The hard right (which would oppose any Obama nominee) is attacking, even stirring up a bizarre controversy about Kagan’s sexuality, which the Washington Post reported this way:

The White House ripped CBS News on Thursday for publishing an online column by a blogger who made assertions about the sexual orientation of Solicitor General Elena Kagan, widely viewed as a leading candidate for the Supreme Court.

Ben Domenech, a former Bush administration aide and Republican Senate staffer, wrote that President Obama would "please" much of his base by picking the "first openly gay justice." An administration official, who asked not to be identified discussing personal matters, said Kagan is not a lesbian.

CBS initially refused to pull the posting, prompting Anita Dunn, a former White House communications director who is working with the administration on the high court vacancy, to say: "The fact that they’ve chosen to become enablers of people posting lies on their site tells us where the journalistic standards of CBS are in 2010." She said the network was giving a platform to a blogger "with a history of plagiarism" who was "applying old stereotypes to single women with successful careers."

The network deleted the posting Thursday night after Domenech said he was merely repeating a rumor. The flare-up underscores how quickly the battle over a Supreme Court nominee—or even a potential nominee—can turn searingly personal. Most major news organizations have policies against "outing" gays or reporting on the sex lives of public officials unless they are related to their public duties.

Mainstream conservatives are somewhat more issue-oriented in their critique. But they are busy outlining arguments—some thoughtful, some crude—for opposition on the National Review Online’s  "Bench Memo" blog.

For the most part, however, the conservative criticism rings hollow.

The general sense is that Kagan would be more cautious and far more centrist than Stevens, a Republican appointee who eventually became the steadiest liberal on the court.

The point here is to suggest that Kagan is some kind of closet right-winger. Her record does not suggest that.

Unfortunately, the same record that does not suggest Kagan is a right-winger also does not suggest that she is serious about controlling against excesses and abuses by the executive branch.

At least initially, the question progressives should ask is whether Kagan is an adequate replacement for Stevens—especially on the critical question of restoring the system of checks and balances that was so severely battered during the Bush years.

Despite all the talk about social and even economic issues that may come before the court, the core question of whether a nominee is inclined to defend the basic premises of the Constitution must always  take precedence. This is even more true today, as the court has fallen under the sway of Chief Justice John Roberts, arguably the most extreme judicial activist to hold the position in modern times.

Under Roberts, the court has done a lousy job of providing judicial support for a reasonable separation of powers.

And the fights are only beginning.

As such, Kagan’s approach to the checks-and-balances debate deserves serious attention from senators who take their constitutional duty to provide "advice and consent" seriously.

The assessment from Cohn, one of my frequent allies in the fight for executive branch accountability,is anything but reassuring.

Before Monday’s announcement by Obama, Cohn argued that: "If he wants to choose a non-judge, Obama could pick Harold Hongju Koh or Erwin Chemerinsky, both brilliant and courageous legal scholars who champion human rights and civil rights over corporate and executive power. Unlike Kagan, whose 20 years as a law professor produced a paucity of legal scholarship, Koh and Chemerinsky both have a formidable body of work that is widely cited by judges and scholars."

Decrying a Kagan nomination as a case of "(taking) the cautious route, Cohn offered some historical perspective that is worthy of note.

"The Warren Court issued several landmark decisions. It sought to remedy the inequality between the races and between rich and poor, and to curb unchecked executive power. Chief Justice Earl Warren wrote these words, which would later become his epitaph: "Where there is injustice, we should correct it. Where there is poverty, we should eliminate it. Where there is corruption, we should stamp it out. Where there is violence, we should punish it. Where there is neglect, we should provide care. Where there is war, we should restore peace. And wherever corrections are achieved, we should add them permanently to our storehouse of treasures," the former NLG president wrote.

"Conservatives decry activist judges—primarily those who act contrary to conservative politics," Cohn continued. "But the Constitution is a short document and it is up to judges to interpret it. Obama has defensively bought into the right-wing rhetoric, saying recently that during the 1960’s and 1970’s, ‘liberals were guilty’ of the ‘error’ of being activist judges. Rather than celebrating the historic achievements of the Warren Court—and of Justice Stevens—Obama is once again cowering in the face of conservative opposition.

Supreme Court nominations take unexpected twists and turns, and nominees who seem disappointing can turn out to be fine justices—just as seemingly impressive picks fall short.

But the concerns that have been raised with regard to Kagan merit serious questioning by members of the Senate Judiciary Committee. Even in an election season, when the rush to confirm will be intense, and when there will be an inclination to back the nominee simply because her Republican critics are so offensive and unreasonably in their attacks, the first duty of evenry committee member, and indeed of every senator, is to derermine whether Kagan can be counted on to restore proper — and real — checks and balances.