PRESIDENT BUSH'S endorsement last week of a constitutional amendment preserving the current understanding of marriage, and the decision of John Kerry and other leading Democrats vehemently to oppose it, ensures that the marriage debate will be front and center in American politics. And it will be prominent not just in 2004, but very likely for a number of election cycles to come.

Until recently, that seemed far from certain. One year ago, gay marriage looked too radical to enter mainstream debate as early as 2004. One week ago, with the photogenic mayor of San Francisco and other local officials rushing to violate state marriage laws with minimal judicial or political opposition, it seemed possible gay marriage would become the American norm with little serious opposition, much as happened with no-fault divorce in the early 1970s.

The seeming paradox traces to one cause: Rarely has there appeared an issue where the gap between elite and popular opinion is so great. A year ago, it was Democratic elites, including and perhaps especially those sympathetic to gay marriage, who wanted to keep this issue in the closet. A week ago, many Republican elites found the idea of capitulating to gay marriage far more attractive than fighting it. Judging from their statements in the wake of the president's announcement, many House and Senate Republicans still hope the issue will fade quickly enough that they won't have to vote on the marriage amendment this year. They are likely to be disappointed.

This is because, in the face of media and elite sympathy for gay marriage, a huge swath of popular opinion appears to be hardening its opposition. Millions of voters are not simply disapproving, as they might be of the Super Bowl halftime show. They seem prepared to change their votes to the extent the marriage debate becomes politically central. For weeks, respected GOP pollster Bill McInturff, not known as a social conservative, has been sharing results of a national poll showing a 4-point Bush lead turning into a 15-point lead should a fight over the definition of marriage become a prominent campaign issue.

Emergence of the marriage debate as the dominant values issue of 2004 is good news for Bush and his political team. It comes at a time when the other two big issue clusters, foreign policy and economics, have become (at least for now) a more even matchup between Bush and Kerry--foreign policy because of our inability to find weapons of mass destruction in Iraq, and the economy because surprisingly few new jobs are so far being created in the midst of a growing economy.

Yet despite the readiness of Democratic and media elites to attribute the president's announcement last week to opportunism, hardly anyone who has spoken to or closely observed the president believes he was eager to engage on this issue. Few politicians welcome a near-universal bad press, which is a certainty for serious opponents of gay marriage. The palpable anger of the White House press corps that accompanied every question in press spokesman Scott McClellan's briefing the day of the president's announcement bore witness to that.