Behind the Senate's long-running impasse over the judicial nomination of Miguel Estrada is a broader struggle over President Bush's aggressive exercise of power on Capitol Hill, which has emboldened Republicans, enraged Democrats and prompted a bitter confrontation between them.

This broader concern helps explain why the fight has been so fierce and why the test of wills is unlikely to end with the confirmation, rejection or indefinite delay of Estrada's nomination to the U.S. Circuit Court of Appeals for the District of Columbia.

Since the Democrats' filibuster to block a vote on the nomination began nearly a month ago, attention has focused on Estrada, his Hispanic heritage, his conservative outlook, the adequacy of information about his views, and implications for Bush's efforts to appoint more conservative judges.

The key dispute has centered on Democrats' complaints that Estrada exemplifies an attempt by Bush to "pack" the federal courts with conservatives, which Republicans dismiss as a Democratic "litmus test" to bar judges who would rule against them on issues such as abortion rights. This argument is intertwined with -- and reinforced by -- a seething frustration among many Democrats over what they regard as Bush's cavalier treatment of the GOP-controlled Congress on issues ranging from Iraq to domestic spending priorities.

The net effect, they say, is to trample over the legislative branch's constitutional prerogatives and upset the delicate system of checks and balances that the nation's founders created to preclude abuses of power. In the end, some contend, this could lead to Bush dominating all three branches of government, with his impact on the judiciary lasting long after he leaves office.

As Democrats see it, Bush expects Congress simply to "rubber stamp" his policies and nominations now that Republicans control both houses.

"There is a kind of noblesse oblige, a sense that he knows best and we should all just fall into line," said Sen. Dianne Feinstein (D-Calif.), a member of the Judiciary Committee, whose Democratic members voted unanimously against Estrada. "I do not believe he takes the United States Senate seriously at all."

"One of the reasons we [Democrats] have held together on Estrada is the feeling that there is such arrogance toward Congress" on many important issues before the White House and Congress, including anti-terrorism policies, said Sen. Charles E. Schumer (D-N.Y), also a member of the judiciary panel. "It's unified, strengthened and energized us."

Bush sometimes seems to employ the same kind of "unilateralist" approach in dealing with Congress that he uses in pursuing war plans against Iraq, Schumer said.

"He treats us like he treats France," grumbled a Democratic aide.

Republicans acknowledge that Democrats feel aggrieved over Bush and his relations with Congress. "They've worked themselves into a real frenzy over it," said one. But they dispute the validity of the Democrats' claims and suggest they are still suffering from post-election trauma.

"That's an excuse, not a reason," said Sen. Robert F. Bennett (R-Utah), speaking of Democrats' complaints about Bush's style in dealing with Congress.

Bennett recalled that a colleague calmed him down when, shortly after arriving in the Senate, Bennett had a complaint about President Bill Clinton. "Popular presidents get what they want, and unpopular ones don't," the colleague told Bennett.

And now, Bennett said, "the thing that's really sticking in their craw is that they are dealing with a popular [Republican] president who gets what he wants."

If Bush is pushing hard for swift action on his nominees, it is because Democrats deferred action on a number of them, including Estrada, when they controlled the Senate, said Judiciary Committee member Jeff Sessions (R-Ala.). "Perhaps they're just responding to the demands of hard-left groups . . . who are taunting them," Sessions said.

On most issues involving presidential powers, Bush can count on support from Republicans even if they disagree. In some cases, such as the judicial squabbles, Bush's defiance appears to have increased GOP lawmakers' resolve.

Bush had major victories during the last Congress, even during the 18 months the Democrats controlled the Senate. While Democrats complained that his idea of bipartisanship was to pick up a Democratic vote or two, conservative Republicans often griped about deals he cut with Democrats on issues such as education policy. Some Democrats fumed that some anti-terrorism policies were imposed without congressional assent, and there were complaints about the lack of true consultation as the administration prepared for war.

Bush appeared to become even less collaborative after the GOP won control of the Senate as well as the House last November, Democrats said. He began by insisting on having his way on the huge domestic spending bill that moved through Congress in January. But it was the administration's handling of judicial nominations, especially Estrada's, that brought the Democrats into open rebellion.

While Republicans describe Estrada as an immigrant success story, Democrats say the 41-year-old Honduran-born and Harvard-educated lawyer was a blank slate, kept that way to hide an outside-the-mainstream approach to important legal issues. Democratic senators demanded more answers from Estrada and more documents from the Justice Department, including internal memos he wrote while working in the solicitor general's office in the 1990s. Without them, Democrats said, Estrada would face a filibuster, requiring 60 votes to break in the 100-member Senate.

The White House has made Estrada available to individual senators but not for another appearance before the Judiciary Committee, and it has refused to release the memos, calling them confidential working documents. The White House cites a letter from the seven living former solicitors general opposing public disclosure of such papers. Democrats cite several cases in which other administrations have handed them over.

Both sides are arming themselves with the weight of precedent that could tip the balance of power for future confirmation battles.

Democrats say that unless they hold the line on Estrada, the Bush administration will try to ram through other judges -- perhaps including a Supreme Court justice or two -- without giving the Senate enough information for the kind of informed consent envisioned by the Constitution.

Republicans, noting that no judicial nomination has been killed by filibuster in 30 years, say such a fate for the Estrada nomination would set a new 60-vote threshold for any seriously contested judicial nominees, slowing the process and depriving the federal bench of some interesting legal minds.

Debate on Estrada will resume Monday, with no end in sight. Republicans have talked about scheduling a vote to end the filibuster, but they remain five votes short of 60. Democrats say only two of these votes are in doubt.