This midterm election presents Rove with a particularly difficult challenge. Beyond testing his reputation for always finding a way to win, the outcome could determine the extent of Bush's influence for the rest of his presidency and shape the way he is perceived by history. Rove has warned associates that a Democratic takeover in Congress would mean an end to Bush's legislative hopes and invite two years of potentially crippling investigations into the administration.

The White House said that Rove would consider an interview for this article if it were conducted off the record, with the provision that quotes could be put on the record with White House approval. The New York Times declined.

The diminishment in Rove's influence reflects the fact that his power is to some extent a function of Bush's popularity. In some cases, Republican candidates have made a deliberate strategic decision that the way to win is to distance themselves from the White House.

But a central problem, Republicans said, is that Rove is seen as juggling two potentially conflicting agendas: Protecting the president's legacy and taking steps to help Republican candidates win re-election.

Rove enters the campaign season after a year of personal tumult. Until mid-June he faced the threat of indictment in the investigation into the leak of a CIA officer's identity, and in April, he was stripped of some of his duties in the White House. Rove was moved from a West Wing corner suite to a smaller windowless office across the hall, a shift one friend said he found demoralizing.

Rove's associates said that throughout the leak investigation, he was coiled and withdrawn. They said his demeanor brightened the moment he learned he would not be indicted. Associates described him as displaying relentless optimism about an election that is filling Republicans with a sense of doom.

Rove determines the bulk of the president's schedule and is a crucial figure in determining what Bush should say this fall. He is the White House's main conduit to conservatives whose willingness to turn out at the polls could help determine the party's success.

Rove has become a star fund-raiser for the Republican Party, raising $10,357,486 at 75 events in 29 states, according to the Republican National Committee. Rove runs regular White House meetings, typically at 6:30 a.m. in the White House mess, reviewing high-profile House and Senate races with the White House political director, Sara Taylor, and sometimes with congressional leaders. He shares his view of the landscape with Bush in a daily 8:30 a.m. briefing.

Rove — with Ken Mehlman, the Republican National Committee chairman, and Taylor, both of whom have assumed a higher profile than in past years — has settled on a narrow strategy to try to minimize congressional losses, while tending to Bush's political strength.