Rupert Cornwell: This civil war spells only bad news for the US in the long term

The US faces huge challenges best settled by compromise and bipartisanship. These are anathema to the Tea Party

The Republican Party has got what it asked for: civil war. That is the main message of the US primary season which wrapped up this week, and it may be very good news for the Democrats in the short term. But it is very bad news for America in the longer term.

Primaries, when voters choose each party's candidate for the general election, normally pass virtually unnoticed in a non-presidential year. They tend to be a hodge-podge of local contests, with no discernable national pattern, the feeblest of curtain-raisers for the main event on the first Tuesday in November. Not however in this year of America's discontent, 2010.

Christine O'Donnell's shock victory in the Republican Senate primary in Delaware is but the most spectacular success of the ultra-conservative Tea Party movement in its challenge to an establishment that has lost control of the party.

But for this debacle, the Republican leadership has only itself to blame. Since President Obama took office in January 2009, backed by solid Democratic majorities on Capitol Hill, the Republican response has consisted of a single word: No. It has done its utmost to block every piece of legislation Democrats have brought forward, and offered no ideas of its own. Up to a point, the tactics have worked. At mid-term elections, voters almost always let off steam, punishing the party in power. This year, given their frustration and anger over the struggling economy and high unemployment, they will do so more than ever.

But the absence of policy has created a Republican vacuum into which the Tea Party, egged on by Sarah Palin and its cheerleaders on Fox News, has moved. The party leadership calculated that the voter enthusiasm generated by the Tea Party tiger would work to its advantage. Now that establishment risks being devoured by it.

Understandably, Democrats are chortling. The party still faces its worst mid-term drubbing since 1994 (when resurgent Congressional Republicans under Newt Gingrich offered a specific platform they called a "Contract with America".) But while the House of Representatives may be lost, the betting is that Democrats will hang on to the Senate – not least due to Ms O'Donnell, whom even Republican strategists admit is too right-wing for voters in a seat Democrats had all but written off.

A divided opposition is also good news for President Obama in 2012. A weak potential Republican field suddenly looks even weaker. Likely candidates like Mitt Romney have kept an embarrassed silence; unchallenged, the antics of Ms Palin, Rush Limbaugh, Glenn Beck et al are more likely to scare wavering voters back to the Democratic fold.

The biggest damage however will be to the good governance of America. The country faces huge structural challenges – reducing the deficit, reshaping energy policy and seeing through healthcare reform to name but three. In the end, under the finely calibrated US political system, such challenges are best settled by compromise and bipartisanship.

But compromise and a readiness to work with Democrats are anathema to the Tea Party. Whatever happens in November, the movement's successes will have convinced incumbent Republicans that safety lies in intransigence. For proof, look no further than John McCain, the 2008 Republican presidential candidate once renowned for his willingness to break party ranks, but who veered sharply to the right to beat off a challenge from the right in the primary for his Arizona senate seat last month.

Moderate Republicans were already a vanishing breed in Washington. The 2010 primaries threaten to condemn them to extinction, and America will be the loser.