“Thoughtful”–the first word out of top aide Karen Hughes’s mouth this morning on NBC’s “Today” show–is a nice adjective to apply to a president. It’s one that has not often been used in the same sentence as George W. Bush, known more for his years as an indifferent student, unworldly businessman and the governor who cut his deliberation over Texas death-penalty cases from half an hour to 15 minutes. As president, Bush has yet to hold a press conference where he showed deep command of the issues or intellectual range. The moniker “Incurious George” was beginning to stick.

Knowing this–and sensitive to the much-publicized calculation that the president has spent more than a third of his time in office away from the White House–key staffers were beginning to worry that Bush was looking a little cavalier about the complexities of the job. That’s where stem cell research comes in. In the five weeks since a cover story in NEWSWEEK propelled the debate into a first-tier national issue, Bush has worked hard to educate himself about the subject and to reflect deeply on the bioethical issues involved.

In his address, penned by chief speechwriter Mike Gerson, who has written under his own byline about moral and ethical issues in the past, Bush did an excellent job of laying out the complications involved. He came across as deliberative, cautious and, yes, thoughtful–all important presidential attributes.

More important, Bush set a strong precedent for the president as explainer in chief. President Clinton gave several speeches where he explained difficult scientific and medical topics (often extemporaneously), but not in prime time with so much public attention. Years from now, when presidents routinely engage such subjects, Bush’s Crawford stem cell speech will be looked back on as a first. To the roles of commander in chief, party leader, top negotiator, budgeteer and First Mourner, any future president will also have to be a science teacher and ethicist.

Even so, this was hardly a “defining moment” for Bush’s presidency. In advance, many pundits saw the decision as a pivot point–the moment when Bush would begin his critical courtship of the middle. By satisfying neither side of the debate, the logic went, Bush would define himself as a moderate and “compassionate conservative.” This is what swing-vote soccer moms want him to be, and they remain the mother lode of American politics.

In the immediate aftermath of the speech, moderate voters are almost certain to respond positively. It will seem as if Bush is accomplishing the first portion of the political repositioning he seeks. But in the months ahead, the facts on the ground–in the labs and universities–will take on more importance than the glow of the speech, and those facts are not necessarily favorable to the compromise Bush offered.

A sign of possible trouble ahead took place last night when Health and Human Services Secretary Tommy Thompson was interviewed on MSNBC after the speech. Thompson, who had favored a less restrictive stem cell research compromise than the one adopted by the president (Sen. Bill Frist’s version, which would have allowed much more research), was loyally spinning for the White House. He claimed that scientists were “extremely happy” with the compromise.

In the past, when stem cell research was a minor issue at best, a politician might have been able to get away with characterizing scientific opinion without fear of contradiction. TV networks shied away from putting scientists on as guests. Too technical and potentially boring.

But now these scientific issues are here to stay. So it didn’t take long for the scientists to go on the air and start punching holes in the president’s logic. After hearing Karen Hughes say that the 60 cell lines would provide “enough work to keep the scientific community very busy,” the “Today” audience heard from someone who knows just a little more about the subject, Dr. John Gearhart of Johns Hopkins University, a top researcher in the field.

“We need a lot more cell lines,” Gearhart said. “They do lose some properties over time, and you have to turn to other lines.” The doctor, echoing scientific opinion around the country, added that the president’s limitations will “delay substantially” efforts to “bring the research to the bedside.”

Because the issue is not going to fade (there’s not a lot else going on these days), the Bush White House may be looking at months or even years of stories about how those 60 existing cell lines are coming along. Are they enough? What if, day after day, nonpartisan researchers called to (planned) congressional hearings complain that their research into curing diseases is being hampered? What if other countries start making stem cell breakthroughs that aren’t allowed in the United States? What if TV pictures show labs throwing out embryos that could have been used for scientific research if only Bush had said yes?

Then the Bush “compromise” might end up defining him in ways he would prefer to avoid. The president could end up inverting the current conventional wisdom, appearing thoughtful but not terribly effective.