year could literally reshape America's democracy.

Veith et al vs Jubelirer involves only Pennsylvania. The state's Democrats have challenged what they say is a rigged and unfair plan to redraw congressional districts, a move approved by Pennsylvania's Republican-controlled legislature after the 2000 census.

But the case's implications are nationwide. At stake is not only control of the House of Representatives in Washington, but the very health of democracy. "This is hugely important," says Sam Hirsch, an attorney for the Pennsylvania Democrats. "Gerrymandering on this scale is corrupting US democracy. This was not what the framers of the US constitution intended."

Gerrymandering is an established American political tradition. Its name derives from Elbridge Gerry, a governor of Massachusetts who in 1811 endorsed an electoral district said to look like a salamander. "Call it a Gerry-mander," a wit said, and the term stuck.

Under the devolved US system, the map of a state's congressional districts is drawn by its legislature - not by a non- political body such as the Boundaries Commission in Britain. Changes are usually made after each 10-yearly national census.

Over the years, partisan gerrymandering has become the norm - traditional spoils for the party which wins control in a state, and then tries to design congressional districts that send the maximum number of its own to Washington.

Democrats have been as guilty as Republicans. But the growing Republican dominance at state level, combined with the wizardry of computers that draw districts to reflect voting patterns down to the tiniest street, has created an unprecedented problem.

By law, districts must be exactly the same size. The idea therefore is to pack as many of the opposing party's votes into as few districts as possible, leaving as many seats as possible in your party's hands. In closely balanced Pennsylvania, Democrats are fighting a scheme which gives a million Republicans control of 10 House seats and the same number of Democrats control of five.

Early this year Texas provided an even more spectacular gerrymandering row, as Democratic legislators fled the state for neighboring Oklahoma. Their aim was to deny the Republican statehouse majority a quorum to push through a plan to redraw districts that would hand half a dozen Democrat-controlled seats to Republicans. In the end the Democrats cracked and the scheme went through. Only the courts can prevent it taking effect.

Nationally, the consequences of gerrymandering on this scale are disastrous. "Voters no longer choose members of the House, the people who draw the lines do," says Samuel Issacharoff, professor at Columbia Law School.

The House of Representatives is almost ossified. Only 20 or 30 of the 435 seats are competitive. Add to that gerrymandering on the scale of Texas and Pennsylvania, and the Republican majority - a narrow 229 to 206 on paper - is all but impregnable.

Gerrymandering has hastened the polarization of US politics. The big threat to an incumbent is often no longer in the general election (81 of the 435 Congressmen ran unopposed in 2002) but at a primary, where radical activists dominate. Incumbents thus become more partisan. Moderate Republicans or centrist Democrats, vital for cross-party co-operation, are threatened species.

Which way the Supreme Court will lean is unclear. The 5-4 ruling in favor of George Bush at the last presidential election shows it does not shrink from political decisions.

In the past gerrymandering has been treated as a fact of life, barred only on racial grounds. "But the fact the justices took this case suggests they believe extreme political gerrymandering needs a second look," Mr Hirsch says. "We're cautiously optimistic."

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