Crawford, Texas ? Frenetic negotiations among congressional leaders, private conversations between President Bush and lawmakers, and a special weekend session over the Terri Schiavo right-to-die case elevated a tragic personal issue into an intense political drama.

But at bottom, the flurry of activity reflected an everyday fact of political life: When a powerful constituency cares passionately about something, all politicians — whether Republicans or Democrats — yearn to respond.

In this instance, the constituency is evangelical Christian conservatives. They played a critical role in re-electing President Bush and swelling Republican majorities in both house of Congress last November, and they have become a voting bloc as essential to the GOP’s new dominance as labor unions and minorities have been to the Democratic Party.

And the pressure on Bush and Republican congressional leaders to respond in the Schiavo case was all the greater because, during the first three months of the president’s second term, social conservatives had become increasingly unhappy with what they saw as neglect of their concerns, such as banning gay marriage, in favor of issues pushed by corporations — changing the bankruptcy laws, curbing medical malpractice awards and opening the Arctic National Wildlife Refuge to oil and gas drilling.

“Our issues aren’t on the front burner every day, but when they are on the front burner it’s on high. The burner is hot and red,” said Louis P. Sheldon, chairman of the Traditional Values Coalition. “This proves that Terri Schiavo was a front-burner issue.”

The very fact that the case of one woman in Florida and the family quarrel over her fate has reached the halls of Congress and captured the attention of the president reflects the power of the evangelical base in setting an agenda, said Richard Cizik, vice president of the National Association of Evangelicals. The Schiavo case, he said, reflected the fact that social conservatives are as consumed with the end of life as they are with pre-born life — and that the politicians are following their lead.

Republicans’ desire to respond to the Schiavo case in a highly visible way was underscored Saturday night when the White House unexpectedly announced that Bush, vacationing at his ranch near Crawford, Texas, would fly back to Washington to sign the emergency legislation aiding Schiavo’s parents in their effort to keep her alive.

Schiavo, who has been severely brain-damaged for 15 years as a result of a heart attack, has been at the center of a legal battle between her husband, who says she had told him that she would not wish to be kept alive under dire circumstances, and her parents, who have sought custody of their daughter.

The case, first taken up by Florida Gov. Jeb Bush and fellow abortion opponents who viewed it as a right-to-life issue, has become a cause for evangelical conservatives nationwide because they see assisted suicide and related procedures as moral and religious issues of overriding importance. Their commitment to the cause has been intensified by rising anger toward her husband and toward the Florida state courts that sided with his position.

On Friday, the pressure on congressional Republicans escalated sharply when a state judge ordered the feeding tube removed and a federal judge ruled that Schiavo’s parents had no legal standing in the federal court system. The legislation that is expected to win emergency approval over the weekend would give the parents standing in federal court, though it would not compel a federal judge to take up the case.