In recent times, British and American politics have often flowed in parallel currents.
Margaret Thatcher's election as prime minister in 1979 was followed by Ronald Reagan's election as president in 1980. As Charles Moore notes in his biography of Thatcher, the two worked together, albeit with some friction, reversing the tide of statism at home and ending the Soviet empire abroad.
They seemed to establish British Conservatives and American Republicans as their nation's natural ruling parties.
In time, Democrats and Labour responded. Bill Clinton's "New Democrat" politics prevailed in 1992, and Tony Blair's New Labourites, adapting Clinton's strategy, won the first of three big national landslides in 1997.
But after any party is in power for an extended period, its wingers start to get restive -- rightwing Republicans and Conservatives, leftwing Democrats and Labourites.
They complain that their leaders failed to enact needed changes and betrayed core beliefs. They take their party's past electoral success for granted and push for a return to ideological purity.
An internal rebellion in the Conservative party overthrew Thatcher in December 1990, and the hatreds it inspired festered for years.
Thatcher's successor, John Major, did win another term in May 1992. But he was hectored by Thatcherite true believers more obdurate than Thatcher had been in office. This intraparty civil war raged through three electoral defeats and only subsided after David Cameron was elected party leader in 2005.
In America, anti-tax conservatives rebelled at George H.W. Bush's acceptance of tax increases in 1990, and Reagan speechwriter Pat Buchanan launched a quixotic challenge of Bush in the 1992 primaries.
That, plus Ross Perot's independent candidacy, led to Bush's loss to Clinton that November. Rightwing frustration promptly found targets in the Clinton tax increases and Hillary Clinton's health care plan, and Newt Gingrich's Republicans captured the House in 1994.
Then Bill Clinton's successful negotiations with Gingrich caused discontent on the Democratic left. It supported Clinton on impeachment but gave 2.9 million votes to Ralph Nader in 2000, which helped defeat Al Gore.
George W. Bush's bipartisan achievements on education and Medicare and continued spending increases caused distress on the Republican right. It found a voice after he left office in the Tea Party movement, whose anger was directed at "establishment" Republicans as well as at President Obama.
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