Senate minority leader Mitch McConnell has a theory about divided government. It's this: When one party holds the White House, and the other holds one or both houses of Congress, the chances of passing landmark legislation improve dramatically. McConnell cites two examples. The first is the passage in 1983 of a Social Security reform (and bailout) bill that brought President Reagan and Democratic House speaker Tip O'Neill together. The other came in 1996 when President Clinton signed a sweeping welfare reform bill drafted by a Republican Congress.

A theory held by the leader of the minority party in Congress normally wouldn't be significant. But it is in McConnell's case because he has suddenly emerged as the king of Capitol Hill. Though Democrats control both the House and the Senate, McConnell has greater influence on what Congress passes and in what form than either House speaker Nancy Pelosi or Senate majority leader Harry Reid. So it matters that he believes the circumstances are ripe for reforming immigration and Social Security.

Until McConnell became Senate minority leader, these two issues had been left to President Bush to promote. And it was a fair assumption that Democrats, having seized Congress, would take charge of the immigration issue while keeping Social Security reform off the congressional agenda altogether. But Democrats have dawdled.

Patrick Leahy, the Vermont Democrat and petulant chairman of the Senate Judiciary Committee, inadvertently cleared the way for McConnell on immigration. Leahy said it was up to Bush, not Democrats, to act first by offering a proposal. He implied the president was insincere in his support for comprehensive immigration reform, which the entire pro-immigration community and other Democratic senators know is untrue.

McConnell stepped in. His goal on most issues is to maximize Republican power by unifying as many of the 49 Republican senators as possible behind a single position. This is necessary to block Democratic legislation because a successful filibuster requires 41 votes. On immigration, however, McConnell's "personal preference" is to pass reform legislation, not block it. And he is well on his way to producing a bill that would win the support of Republican senators from John Cornyn of Texas, a restrictionist, to John McCain, who cosponsored a liberal immigration bill last year with Democratic senator Edward Kennedy. This year Kennedy has complained that McCain is avoiding a discussion with him about immigration.

At McConnell's instigation, Republican senators have been meeting for weeks to discuss immigration reform. The group includes Lindsey Graham of South Carolina, Jon Kyl of Arizona, Mel Martinez of Florida, and Johnny Isakson of Georgia. Isakson is important because the Republican bill now taking shape is centered around his idea of staggering reform by doing border security first, then taking steps to deal with the illegal immigrants who are already here.

The latter steps would be pursued once the Department of Homeland Security certified that five measures necessary to border security had been undertaken. These include the hiring of 14,000 new Border Patrol agents, authorizing the construction of 370 more miles of fence along the border with Mexico, deployment of unmanned aerial vehicles, deployment of ground radar, and the creation of a biometric ID card so employers can verify whether an immigrant worker is legally in the country.