Britain's Prime Minister David Cameron delivers a speech to placard waving Conservatives during an European election campaign rally at a science park in Bristol

Establishment Republicans have been delighted by the victory of Thom Tillis, their favored candidate in last week’s North Carolina primary. After expensive advertising campaigns by establishment bagmen like the U.S. Chamber of Commerce and Karl Rove’s American Crossroads, mainstream conservatives believe they have a candidate who can beat Democrat Kay Hagan to win a valuable Senate seat in November.

Some commentators see Tillis’s triumph as a sign that other impending GOP primary races will also deliver electable candidates. Having watched the Senate slip from Republican grasp in 2012, as Tea Party candidates such as Todd Akin in Missouri, Christine O’Donnell in Delaware and Richard Mourdock in Indiana depicted the party as too extreme, they say the Tea Party is in retreat.

Not so fast. The experience of conservative parties elsewhere suggests that when pragmatists triumph over dogmatists, the dogmatists either regroup and go on to overwhelm the moderates, eventually making the party their own. Or they set up their own party — and trounce the moderates at the ballot box.

ThatcherThat is happening in Britain. The Conservatives, once Britain’s natural governing party, find themselves about to be pressed into third place in the European Parliament elections. They will be runners-up not only to the Labor Party but also to the populist United Kingdom Independence Party, their ideological nemesis. Like the Tea Party, the Independence Party has set itself up as the true conscience of conservatism.

There was a time when the European left was riven over dogma, with middle-ground Social Democrats jostling with hard-line Socialists. In Britain through the 1970s and 1980s, there was a three-way split, with middle-of-the-road Labor candidates noisily fending off assaults from the far left as well as Social Democratic reformers. This left Margaret Thatcher’s Tories free to win three elections in a row.