America goes to the polls today in the crucial mid-term elections that decide the political make-up of Congress. The results to be announced tomorrow and on Thursday, will also determine whether President Bush will face increasing opposition or support during the remainder of his term. Elaine Monaghan, left, in Washington weighs up what is at stake.

Why are these elections held?

The US Constitution requires Americans to elect a new House of Representatives every two years, and at the same time to hold elections for a third of the seats in the Senate, or upper house, whose members have a six-year term. Today's polls are called mid-terms because they are taking place half-way through the four-year presidential cycle.

Why are they important to President Bush?

The outcome could give Mr Bush a solid foundation for re-election in 2004, or, if the Democrats take back the House and keep the Senate, leave him battling to set a legislative agenda. Most analysts expect the outcome to be a status quo, but small, unexpected changes could have a big impact - especially bearing in mind the traditionally low turnout.

One area where the Democrats could win an advantage is in the gubernatorial elections taking place in 36 states, where candidates could pay for America's economic woes. Many of these races are expected to be tight. A governor can provide crucial help in a presidential race by providing a campaigning infrastructure in key states.

What is the current balance of power between the Republicans and the Democrats?

Although Mr Bush is riding high in opinion polls, above normal mid-term rates, the control of Congress is very finely balanced, with Democrats holding a one-vote majority in the 100-seat Senate.

The Republicans hold 223 of 435 seats in the House, while the Democrats have 208 seats and one seat is filled by an independent, who associates himself with the Democrats. Three seats are vacant. The Democrats need to gain six seats to win back the House.

Historically, though, it is extremely rare for the House to change hands - the Democrats held it for 40 years until 1994 - and the Republicans are counting on holding a majority, despite an historical tendency for the party not in the White House to pick up seats.

Equally, Democrats are considered to be in a better position to hold on to their control of the Senate. Only about 50 House races are considered highly competitive and 13 are too close to call, according to statistics gathered by Congressional Quarterly, an insider Washington journal that closely follows events on Capitol Hill.

The Senate, however, is more competitive, with six of the 34 races considered dead heats and seven more seen as highly competitive, according to Congressional Quarterly.

What are the key issues?

September 11 and its aftermath, and the possibility of war with Iraq, have all but eclipsed the elections, to the point where there is no single issue dominating the campaigns.

A slim majority of Democrats in the House voted against a resolution authorising use of force in Iraq in October, but they have been loathe to criticise the President on national security issues, including Iraq. Recently however, the Democrats have turned their attention to the economy, citing higher unemployment, a sinking stock market and shrinking pension plans.

The vote on use of force in Iraq dragged on well into the campaign period, creating anxiety among Democrats who had wanted economic issues to dominate the front pages. The conventional wisdom is that economics trumps national security in American elections, but since September 11, the lines between foreign and domestic issues have become blurred. However, Mr Bush's popularity since September 11 does give Republican candidates an advantage by providing them with a shield to run behind.

Where are the key battlegrounds?

An aircraft crash last month that killed Senator Paul Wellstone, a Minnesota Democrat and prominent liberal, has focused attention on the election battle there and left it wide open. Walter Mondale, 74, the former Vice-President to Jimmy Carter, has stepped in to try to fill Mr Wellstone's shoes, but his popularity is not clear.

In South Dakota the Senate race is also attracting attention because it is the home state of Tom Daschle, leader of the Democratic majority in the Senate. In a measure of the importance being attached to this battle, Mr Bush this week made the first presidential visit to South Dakota since 1936, prompting observers to portray the campaign as a proxy war between the President and Mr Daschle.

Supporters of the incumbent, Tim Johnson, a Democrat, wear badges saying a vote for him is a vote for Mr Daschle. While the Republican challenger, John Thune, uses Mr Bush in his campaign advertisements.

Another key battle will be for the Governership in Florida, where Jeb Bush is facing a challenge from another Democrat, Bill McBride, but is currently ahead in the polls, helped by repeated campaign visits from the President, who also happens to be his brother.

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