In the south-western US state of Nevada, Democratic Senate leader Harry Reid is facing the fight of his political life, running in a dead-heat with Republican candidate Sharron Angle.

Reid has held his Nevada Senate seat since 1987. He won re-election in 1992, 1998 and 2004, and became Democratic leader in the Senate following the 2004 election, when his predecessor Tom Daschle lost his own Senate seat. Reid has served as majority leader since the Democrats gained a majority in the Senate at the 2006 mid-terms.

Reid has presided over a difficult period for Senate Democrats. Despite a super majority of 60 senators throughout 2009, along with a new President with popular support and a large majority in the House of Representatives, much of the Democratic legislative agenda has foundered in the Senate.

Reid’s hold on his Nevada seat has often been precarious. He won narrowly in 1986 and 1998, with his Republican opponent in 1998, John Ensign, going on to win Nevada’s other Senate seat in 2000, and winning a second term in 2006. Nevada has gone with the winner in every Presidential election since 1980, and Republicans have served as Governor since 1999. With support for Democrats declining in the lead-up to this year’s election, Republicans were confident of defeating the Democratic Senate leader for the second time in six years.

Reid’s only prospect of political survival came out of the Republican Senate primary, with controversial former state assembly woman Angle winning the contested primary.

Angle has a reputation as a particularly extreme Republican politician. In the past she has campaigned for US withdrawal from the United Nations and the privatisation of Medicare. She gained a reputation in the Nevada Assembly as often being the only member to vote against legislation that had gained broad consensus. Recently she made claims that two US cities were under sharia law, which was rebuked by those cities’ mayors.

Reid has proven much more difficult for the Republicans to defeat than first thought. Reid has had some success defining his opponent as an extremist, and has managed to claw back ground in the race, with a much larger campaign budget.

While Angle had a small but solid polling lead in earlier months, her lead has disappeared. Out of 10 polls of likely voters in Nevada in the last month, no poll has produced a lead of more than 4% for either candidate, producing an effective dead heat. Nate Silver, of FiveThirtyEight, gives Reid a 44% chance of retaining his seat.

Nevada is one of the races that is proving to be key to this year’s election. To gain a majority, the Republicans need to gain 10 Democratic seats. The Democrats look almost certain to lose five seats, while another four, including Nevada, are now extremely close races. If the Republicans can gain those four toss-up seats, and pull off one more win, they will produce a 51-49 majority in the Senate.

The Democrats now appear to be on track to lose their majority in the House of Representatives, and they seem set to lose the Governorship in many states in the lead-up to critical redistricting battles. The Nevada Senate campaign may prove critical in preserving the power of the Democrats as President Obama begins to gear up for his re-election.