Rep. Mike Castle’s upset loss in the Delaware Republican Senate primary Tuesday sent another shock wave through the party’s dwindling moderate ranks and had Democrats crowing that the Republican Party’s big tent had collapsed.

Rep. Patrick Tiberi, a moderate Republican from an Ohio district won by President Barack Obama, said that if Christine O’Donnell, the tea party candidate who beat Castle, loses in November as many now expect, there will be blowback against Sen. Jim DeMint (R-S.C.), Sarah Palin and others who endorsed her. “There will be Republicans, including conservative Republicans, who will ask why would you endorse a flawed candidate? If we come one seat short of taking control of the Senate, that will be one that comes back and haunts us.”

“It doesn’t help for us to turn on each other,” said Rep. Bob Inglis (R-S.C.), a conservative who was nonetheless defeated in a tea party purge earlier this year. “It doesn’t help us to hold purity meetings. I just don’t know how you build a party … by subtraction.”

Inglis said that in the modern Republican Party, you have to “pass the Glenn Beck test. … You have to say the country is all going to pot, with a little tear in your eye.”

“We’re all supposed to be angry and sell conservatism with a snarl,” Inglis said. “I wonder if people like Ronald Reagan and Jack Kemp could survive in this environment.”

Rep. Charlie Dent (Pa.), one of the more moderate House Republicans, said Republicans need to remember that the country is a center-right country. Conservatives are ascendant right now, he acknowledged, partly in reaction to a very liberal Democratic majority, he said. But Dent said he will continue to remind Republicans they have to appeal to both conservatives and moderates. “We’ll need both groups to win and we’ll need both groups to govern,” he said. “We need a center-right agenda.”

Tiberi said that despite high-profile defeats such as Castle’s, moderates have been successful in a number of House primaries and he believes the ranks of moderate Republicans will grow in November.

Tiberi said Republicans can’t win without moderates. “I don’t think the majority of districts can elect Jim DeMint Republicans,” he said.

The rule should be to elect the most conservative Republican who can win the district, Tiberi said. He also noted that purges are going on in both parties, with some Democrats who voted against the health care bill being shunned by unions and other liberal groups.

Former Rep. Tom Davis (Va.), who now heads the Republican Main Street Partnership, which promotes moderate values candidates, said, “The political parties are shrinking. … The moderates are peeling off and becoming independents. It’s happening in both parties.”

[IMGCAP(1)]Davis said some elected officials are afraid to deviate from their base for fear it may come back to haunt them in their next primary election, which impedes Congress’ ability to get things done as Members are unwilling to compromise.

Main Street spokesman Chris Barron added that the current environment has forced a redefinition of the word “moderate.” His organization doesn’t have fewer members this year, it’s just that their philosophies are changing.

The days have passed when Members such as ex-Sen. Lincoln Chafee (R-R.I.) and ex-Reps. Wayne Gilchrest (R-Md.) and Christopher Shays (R-Conn.) could live in the political middle, Barron said.

“Those types of members don’t really exist any more,” he said. “The centers of both parties have moved — Democratic Party more to the left and the Republican Party to the right.”

Main Street’s political action committee supports 24 “centrist” GOP Members or candidates this election cycle.

They include people in swing districts such as Lou Barletta, the Republican challenging Rep. Paul Kanjorski in Pennsylvania’s 11th district, Jim Renacci (R), who hopes to knock off Rep. John Boccieri (D) in Ohio’s 16th, and former Rep. Charlie Bass of New Hampshire, who proved Tuesday that a moderate Republican can still win a GOP primary against a conservative.

Bass beat Jennifer Horn by 6 points and became the instant favorite to take over the 2nd district seat left open when Democratic Rep. Paul Hodes chose to run for Senate.

Conservative Republicans said moderates need to listen to their base and not embrace things like the cap-and-trade bill that Castle voted for.

“It’s not enough to be a nice guy like Mike,” Rep. Louie Gohmert (R-Texas) said. “I hope the message is to read the bills, be careful about the bills, and be careful about the damage you are doing to our economy before you vote.”

Rep. Jeb Hensarling (R-Texas) said Members need to heed the concern of voters that the country is headed toward bankruptcy. “If you vote contrary to your voters, they have the option of retiring you,” he said.

Hensarling also said the defeat of moderates such as Castle could have the advantage of making the Republican Party more conservative and cohesive next year.

A Senate Republican aide said the Castle defeat should put moderate Senators such as Olympia Snowe (Maine) on notice, if they weren’t already after the defeats of Sens. Lisa Murkowski (Alaska) and Bob Bennett (Utah).

“Revolutions are messy,” the aide said. “It’s exciting and scary. It’s like trying to hold a live wire. Any incumbent Republican who does not work their tail off to get reelected, and do what John McCain did … they deserve to lose.”

Retiring Sen. George Voinovich (R-Ohio) said Castle had been successful in Delaware because he was more liberal than other Republicans and could appeal to the state as a whole. “Do you … say that you have to be a purist, and if you don’t do that, that we’d rather have a Democrat? There needs to be a more moderate voice speaking about the fact that this is a big country with a lot of diverse opinions, that we Republicans have different strains in us, like Democrats do, and what we should be doing is trying to figure out what those common strains are, because that’s where we should be spending our time if we expect to be successful.”

But Republican Conference Chairman Mike Pence (Ind.) was quick to praise O’Donnell and urged the party to support her.

“I hope that the next Congress we get serious about fiscal discipline and reform and seeing conservative candidates win primaries is what we call a good start,” Pence said.

And House Minority Leader John Boehner (R-Ohio) called O’Donnell’s victory a part of the rebellion he says is going on across the country. “I’ve never seen more Americans engaged in our government in my lifetime. The voters of Delaware have spoken and you are going to continue to hear the American people speak not just last night, but you are going to hear them speak loud and clearly come November.”

But Democrats said the Delaware result would help Democrats hold on to their majorities.

“The Republican Party just hung out a big sign saying no moderates, no independents welcome,” Democratic Congressional Campaign Committee Chairman Chris Van Hollen (Md.) said. Van Hollen said moderate Democratic incumbents have won their primaries, while a series of conservative upsets in Republican primaries have opened up opportunities for Democrats.

He said Republicans haven’t learned the lesson from their purge of moderate Republican Dede Scozzafava in New York earlier this year, which threw the seat to Rep. Bill Owens (D).

Steve Peoples, David M. Drucker and Anna Palmer contributed to this report.