For the first and only time in a remarkable political career — which began in 1966 when he captured a “safe” Democratic state legislative seat in Delaware and included winning campaigns for the state Senate, for lieutenant governor, for two terms as governor and then nine terms to the House of RepresentativesMike Castle, on a Tuesday night in September 2010, lost an election.

Mark Shields

Mark Shields

In the crowd of admirers who heard him concede, there were more than a few tears, some disbelief and a ton of anger.

Joe Meloy, 76, a veteran Republican activist in Delaware, was solemn: “Mike Castle is totally principled, the finest gentleman in the world.” And the Tea PartyRush LimbaughSarah Palin-backed opponent who defeated him, Christine O’Donnell? “She’s a flake — a complete whack job.”

There was understandable fury at Limbaugh’s ugly smear on his election-day radio show that Castle in 2008 had nefariously supported sending a resolution calling for the impeachment of President George W. Bush to the Democratic-controlled House Judiciary Committee. Limbaugh deliberately chose to ignore the fact that two of Bush’s strongest fellow conservatives, Reps. Kevin Brady and Sam Johnson, both R-Texas, along with the senior Republican on the House Rules Committee, Rep. David Dreier,R-Calif., voted with Castle to send the impeachment resolution to legislative oblivion, where, as they intended, it died a silent death.

It must first be acknowledged that the Tea Party has brought both dramatically increased numbers and enormous energy to the 2010 Republican primaries. True, with Castle’s defeat, Democrat Chris Coons is now heavily favored to win the Delaware U.S. Senate seat Democrats had privately conceded to Castle before O’Donnell pulled her upset. But as Democrats learned in the 1970s, the newcomers’ energy and enthusiasm comes with a stiff price for the party.

Forty years ago, the issues and the causes and the constituencies were different: fierce, largely youthful opposition to the Vietnam War, uncompromising supporters of abortion rights and gay rights, and environmental activists. But the same fever of abolitionist morality — seen in the current Tea Party — characterized the “New People” to politics who then, as now, were free of self-doubt and brimming with passion and a sense of their own rectitude.

President Ronald Reagan’s “80 percent rule” — that someone who votes with you 80 percent of the time is an ally and a friend and not a 20 percent traitor — is heresy to all Tea Party types. In their unreflective conviction, cooperation on any issue with those on the other side is disloyal and compromise of any kind is treasonous.

After the “New People” — the insurgents, whether on the Democratic left or the Republican right — prove by their energy and numbers they can defeat a targeted incumbent in a primary, other elected politicians and party leaders are terrified. They quickly sue for peace with the activists, embracing their agendas and being overly careful never to make them angry or even unhappy.

This was the case from 1972 forward in the Democratic Party presidential nominating contests. Candidates relentlessly, even shamelessly, solicited the blessings, if not the endorsements, of the antiwar, pro-choice, gay rights and environmentalist lobbies. A veto from one of them could cripple a Democrat’s White House prospects.

Look for the 2012 Republican presidential field to totally embrace the Tea Party program. The only place you will find the word bipartisan will be in the dictionary. Candidates, ignoring the contradictions in their positions, will swear allegiance to a balanced federal budget while simultaneously, and hypocritically, championing trillions more in tax cuts for the most affluent.

Watching the 2012 Republican Party pander to the Tea Party will be dispiriting and politically damaging — and could well be the key to the beleaguered incumbent, President Barack Obama, winning a second White House term.

Remember: If that happens, you heard it here first.

Mark Shields is one of the most widely recognized political commentators in the United States. The former Washington Post editorial columnist appears regularly on CNN, on public television and on radio. Click here to contact him.