Sen. Charles Schumer (D-N.Y.) warned President Bush on Tuesday to open a dialogue with Senate Democrats over the selection of future federal judges or face a renewed filibuster effort to block his nominees.

“The events of last night should be a shot across the president’s bow,” Schumer said of the agreement that kept the judicial filibuster intact. “Consult — and if you don’t … and continue to choose people who are way at the extremes, way off the deep end, then there’s not going to be the comity and smooth sailing for judicial appointments that we all would want.”

Democratic leaders also sent Bush a letter urging him to “engage in real consultation with the Senate on future judicial nominations.”

The letter and explicit threat from Schumer — who chairs the Democratic Senatorial Campaign Committee — came less than 24 hours after a bipartisan group of Senators forged a historic compromise to thwart an effort to eliminate the minority party’s ability to filibuster judicial nominees. It also was one of the many signs that the bipartisan deal is, at best, fragile.

Sen. Trent Lott (R-Miss.) said he was whipping votes in the event the deal falls apart and Republican leaders feel a need to resort to the “nuclear” — or as Republicans call it — “constitutional” option.

“I have already been counting the numbers, and of the seven, I know who was there and who wasn’t there and what it all boils down to,” Lott said. “I am already planning to make sure we have an enforcer of this agreement, and if it falls apart we are going to have the votes for the alternative.”

Throughout the day, individual Senators said they were seeking to understand the nuances of the agreement’s language, while several questioned whether it best served the interests of their respective political parties.

A senior Democratic Senator who requested anonymity said it was wrong for his colleagues to allow a handful of judges to have a clear path to the federal bench.

“We took three of the worst ones and let them go,” said the Senator. “What does that say about our principles?”

Across the aisle, there was equal angst by Republicans who felt strongly the GOP needed to change the filibuster rule before a vacancy on the Supreme Court occurs.

“If we had put in place a constitutional option, the folks that lost would have been upset for a while, but at least you would have established the ground rules,” said Sen. George Allen (R-Va.).

Republican strategists and activists echoed Allen’s comments, saying it would be harder to eliminate judicial filibusters in the middle of a Supreme Court battle.

“I think what you are doing is delaying the inevitable and I think that in some ways seven [GOP Senators] have made the decision for the majority not to go onto this terrain, but withdraw and fight another day,” said Tony Perkins, president of the Family Research Council. “Now, I think that the terrain they will eventually fight this issue on will be less favorable.”

Allen said several of his colleagues shared similar concerns, especially since the agreement gives Democrats the option of filibustering nominees in “extraordinary” circumstances. The Virginia Senator predicted that the Senate would need to address it again, perhaps in the near future.

“This is not as well-defined as people say,” Allen said. “It is like a rained-out double header, and we will most likely have to play it again later.”

Senate Majority Leader Bill Frist (R-Tenn.) would not rule out triggering the nuclear option in the future should he believe that Democrats were not following it in good faith.

“The constitutional option remains on the table,” Frist said in a speech delivered from the Senate floor. “It remains an option. I will not hesitate to use it.”

And despite the talk about comity in the Senate as a result of the agreement, the politics did not stop once the deal was struck.

In congratulating the 14 Senators who signed on to the deal, Senate Minority Leader Harry Reid (D-Nev.) also took the opportunity to criticize several Republican leaders, including Frist.

“I want to say a special thanks to the Senators, Democrats and Republicans alike, who had the courage to stand up to the political strong-arm tactics of George Bush, Dick Cheney, Bill Frist and Tom DeLay,” Reid said. “When the waves of outside pressure groups crashed against the marble walls of our Capitol, they stood their ground.”

Senate Republican Conference Chairman Rick Santorum (R-Pa.) responded in kind, suggesting that when Frist sought to negotiate a deal with Reid to avoid the nuclear option, the Minority Leader was not interested.

“Sen. Reid was, without question, carrying an extra agenda of the ACLU and the People for the American Way and the very left-wing organizations that were behind this movement in the first place” Santorum said.

With the disagreement over judges resolved, at least temporarily, the Senate will now turn its attention to the nomination of John Bolton to be the next U.S. ambassador to the United Nations as well as other matters, such as legislation overhauling the nation’s energy policy, a major highway bill and the Defense Department authorization bill.

Democrats also vowed to continue pursuing their top nine domestic agenda items that are designed to aid veterans and women, among others.

Senate Democratic Policy Chairman Byron Dorgan (N.D.) said party leaders are in the process of “developing a framework about what we do after this agreement.”

“We certainly want to be talking about the issues we care about, and if the majority party is not prepared to do that then we certainly are prepared to make that happen,” he said.

Reid will provide more details about the Democrats’ agenda in an address Thursday at the National Press Club, said Reid spokesman Jim Manley. (For lobbyists’ reaction on how the compromise deal on judges may affect the progress of key legislation, see story, page 11.)

Santorum dismissed the Democrats’ vow to move forward with their legislative priorities.

“I fully expect the radical left of the Democratic Party, led by Harry Reid, to continue to be obstructionist and to try and move an agenda that is outside of the mainstream of America,” he said.