According to the US Constitution, one third of the Senate is required to stand for election every two years. This year there are 35 seats being contested (including one special election to fill the seat of a member who recently died). Because the last time this group of senators ran for office was in 2002 - the year George W Bush was able to help win victories for so many members of his party - only 12 of the 35 running are Democrats and 23 are Republicans. With Mr Bush such an unpopular president and the Republican brand tarnished, the task the GOP faces in re-electing its members is a difficult one. Democrats currently hold 50 seats and hope to increase their numbers next month. Were they to take 10 seats away from the Republicans, it would give Democrats the substantial majority they hope to have in the next Congress. This may be difficult, but it is possible. What follows is a look at 11 Senate races worth watching on Nov 4, and why each of these Republican seats might change hands in 2009.
In Virginia, Mark Warner, a former Democratic governor, stands to win easily over his Republican opponent, James Gilmore, also a former governor of the state. Mr Warner was a popular governor, with a record of improving Virginia's economy, sure to be an important issue in this year's election. Virginia, once a strong Republican state, has undergone dramatic changes in recent years, with an influx of new immigrant communities as well as the growth of a liberal upper middle-class suburban population in the northern part of the state. Mr Warner also benefits from massive new voter registration among African-Americans and Hispanics throughout the state. Since the seat being contested was held by John Warner (no relation), a Republican retiring his seat, this represents a near certain pickup for Democrats.
In both Colorado and New Mexico, Democrats have fielded strong candidates against weaker Republican opponents to replace retiring Republican senators. Congressmen Mark Udall in Colorado and Tom Udall in New Mexico (they are cousins) are also beneficiaries of dramatic increases in voter registration among those states' substantial Hispanic communities. With both states having elected Democratic governors, and with Barack Obama, the Democratic candidate for president, in range of winning both, these two also are likely Democratic pickups.
Gordon Smith of Oregon and John Sununu of New Hampshire face tough re-elections largely because of the unpopularity of Mr Bush and the effect this has had on the Republican Party in both states. Mr Smith, a moderate Republican, has sensed such difficulty with the Republican brand that he has distanced himself from his own party and instead tried to tie himself to Mr Obama, going as far as to attempt to have the Republican identification removed after his name on the ballot, and running a television ad showing himself with Mr Obama. Mr Sununu, a first-term Arab-American senator with a strong record in Middle East issues and civil liberties, is in a rematch with Jeanne Shaheen, a former governor whose husband is an Arab-American, whom he defeated in 2002. He faces an uphill battle given the Democratic tide that appears to be sweeping the state - with Democrats having swept the New Hampshire elections in 2006 (winning the governorship, both congressional seats and taking control of both houses of the state legislature for the first time in more than 150 years).
Huge increases in African-American voter registration across the South may help Democrats. Once thought to be a safe Republican region, polls are showing elections there are much closer than before, with Democratic Senate challengers actually out-performing Mr Obama in several states (possibly because of the fact some white Democrats may be more inclined to support a Senate Democrat than to vote for an African-American for president). Democrats are within range of winning in Kentucky, Mississippi and Georgia; and in North Carolina a Democrat, Kay Hagan, holds the lead over Elizabeth Dole, the incumbent Republican senator.
Ted Stevens's 42-year career in the Senate representing Alaska may hinge on the outcome of a corruption trial. Once thought invincible, Mr Stevens has been humiliated by the pettiness of the corruption involved, and the fact that the trial kept him from campaigning for many weeks. If the jury comes back with a not-guilty verdict, he may still win; but if it is guilty, the Democratic candidate, Mark Begich, a former mayor of Anchorage, could take it.
Norm Coleman, a Republican from Minnesota, is currently behind in the polls, with comic-turned-candidate Al Franken leading by a few points. The race is too close to call. Complicating the Minnesota picture is an independent candidate, Dean Barkley, who actually occupied the seat temporarily after the death of Paul Wellstone, and is in a strong third place. Minnesota has a record of unpredictable elections and a political climate favourable to independents. firstname.lastname@example.org