Beyond his Texas home, few states received more of Karl Rove's attention than Pennsylvania.

In 2004, particularly, the state proved to be a laboratory demonstrating both the power and the limits of the political strategy that produced two presidential terms for George W. Bush.

State Republicans who worked with Mr. Rove described him yesterday as a political genius whose planning had elicited unprecedented turnouts among core Republican voters.

"I was one who had questions on whether you could really expand the base that much, as opposed to persuading Democrats and independents," said Leslie Gromis, who was a campaign manager for former Gov. Tom Ridge and a key lieutentant in the Bush campaign's mid-Atlantic states effort in 2004.

"When I saw the turnout numbers from some of those smaller counties, I was shocked. It started in 2003. We had pushed and asked them to do all this grass-roots [work] with team leaders and outreach and it worked."

The late President Richard Nixon is credited with the classic political analysis that a Republican presidential candidate should run to the right during the primaries, then tack back to the broad center in the general election.

Mr. Rove flouted that advice. While Mr. Bush talked of being "a uniter, not a divider," his presidential campaigns, particularly the 2004 re-election that gave him the popular vote majority that had eluded him four years earlier, rested upon an intense focus on mobilizing his party's base voters, social conservatives, while portraying Democrats as weak defenders against a dangerous world.

"He is certainly a brilliant political strategist," Robert A. Gleason Jr., Pennsylvania Republican chairman, said of Mr. Rove. "He pushed the idea of building those constituencies -- pro-life conservatives, 2nd Amendment supporters, the outreach to evangelicals."

Shortly before the 2000 election, Ms. Gromis sat with Mr. Rove in a hotel restaurant in Downtown Pittsburgh and handicapped the state's prospects. The Texan was conversant about the fine details of Pennsylvania politics, from which constituencies appeared most energized to the potential impact of a threatened Philadelphia teachers strike.

His grasp of ground-level details was not confined to Pennsylvania. Mr. Rove established a reputation for familiarity with precinct-by-precinct details of elections across the country. But his focus on Pennsylvania was even more evident in the preparation for Mr. Bush's next campaign. The president became a virtual fixture in the state.

That was the visible part of the campaign. The less public part that Ms. Gromis described was the meticulous, months-long process of one-to-one grass-roots organizing. The effort for which Mr. Bush dubbed him "the architect" included early organizing, goal-setting and reporting of the metrics of people-to-people contacts.

All of that produced the largest number of Pennsylvania votes for a Republican in history -- albeit not enough for Mr. Bush to carry the state. His 2004 total of 2,793,847 surpassed the record Mr. Nixon had set while rolling to a landslide victory over George McGovern.

Senior Pennsylvania Republicans, including Ms. Gromis and former U.S. Sen. Rick Santorum, consoled themselves by maintaining that the effort had forced Sen. John Kerry to devote resources to the state that otherwise might have turned the tide of the Democrat's narrow, and nationally decisive, loss in Ohio.

From a regional as well as national perspective, the enduring political lessons of the Rove strategy may not be clear for several election cycles. Republican candidates were decimated nationally in last year's election, with particularly severe casualties in Pennsylvania, where four GOP incumbents were defeated for Congress.

Ms. Gromis calls Mr. Rove a political master who will be remembered alongside such notables as the Democrats' James Carville and the late Republican Lee Atwater.

"I think the foundation of the strategy will live on," she said.