America’s unofficial end of summer this week marked the unofficial beginning of the campaign that may give Republicans control of the Senate.
It is an outcome that could halt president Barack Obama’s legislative agenda in his final two years in the White House. Republicans already have an unassailable majority in the House of Representatives.
After Monday’s Labour Day holiday, there are just under nine weeks until voters decide on all 435 House seats, 36 of 100 in the Senate and governors in 36 states and three US territories.
The 4 November vote is called a midterm election because it falls halfway through a president’s four years in office. The vote will take place in a political climate that is more deadlocked in partisanship than at any other time in modern history.
Political experts believe, that Republicans are likely to take control in the Senate for a number of reasons. Firstly, the party that holds the White House in a second presidential term historically does poorly in that midterm election.
Compounding that, Republicans, especially the most energised and conservative wing of the party, are far more likely than Democrat voters to turn out on election day.
Secondly, Mr Obama’s approval ratings are hovering in the low 40s and could go even lower given increasing dissatisfaction over his handling of foreign policy.
Russian meddling in Ukraine and the sudden takeover of much of northern and western Iraq by fundamentalist Sunni Muslim fighters of the Islamic State are affecting his popularity.
Mr Obama’s slumping support has caused Democratic candidates in some of the most important races to distance themselves from him on the campaign trail. Republicans are hitting Democrats hard over domestic issues as well, focusing on the US healthcare overhaul known as Obamacare.
Immigration remains an issue and Republicans claim Mr Obama’s plans to sidestep Congress by using his executive powers represent an unlawful power grab.
Finally, Republicans only need a net gain of six seats to capture a 51-49 Senate majority. Three of those are seen as a given in Montana, South Dakota and West Virginia, where incumbent Democrats are not seeking re-election. Democrats in three southern states that Mr Obama did not carry in 2012 are facing stiff challenges.
Experts say Democrats in three Northern states and one in the Mountain West – previously seen as safe – could fall to robust Republican challenges.