If that happens again, let alone if the discrepancy between the vote and the practical result is even greater, the United States will begin to face a genuine legitimation crisis - with Democrats systematically denied political power commensurate with their level of support in the population at large. Here is a dummies guide.
McSally and Sinema are running neck-in-neck in a state which President Donald Trump won by 3.5 percentage points in the 2016 presidential election.
Midterm elections are not the same as state and local elections, which are held yearly. AP and Fox News split from the consortium to launch an alternative called VoteCast, relying on interviews conducted just before the election ― an approach AP says "reflects how Americans vote today: not only in person, but also increasingly early, absentee and by mail".
It's a pivotal moment for Nancy Pelosi - the beginning of a triumphal return as the nation's first female House speaker, or the start of a political reckoning over who should lead Democrats in the Donald Trump era.
Voters also were deciding ballot measures in four states - Colorado, Michigan, Missouri and Utah - that propose to overhaul the redistricting process and reduce the likelihood of partisan gerrymandering by either major party.
The Senate is composed of senators, each of whom represents a single state in its entirety, with each state being equally represented by two senators.
Abrams, who has received the support of Oprah Winfrey and other celebrities, would be the first black woman to become governor of a USA state if she wins.
Right now, Republicans control the Senate by a slim 51 to 49 margin.
Outside a nearby yoga studio where suburban moms were gathering for a workout, another name came up: Supreme Court Justice Brett Kavanaugh, whose confirmation hearings were marked by allegations of high-school sexual assault that Republicans have dismissed as a Democratic smear job. However, out of the 35 seats up for election in 2018, 26 are held by Democrats.
US puts 'maximum pressure' on Iran as sanctions resume
The new American sanctions particularly hurt Iran's vital oil industry, a crucial source of hard currency for its anemic economy. But the sanctions on Iranian oil exports also reportedly exempt several of the world's largest economies.
Democrat Andrew Gillum, 39, the African American mayor of Tallahassee, is locked in an acrimonious battle with Ron DeSantis, 40, a member of the House of Representatives and ardent Trump supporter.
All 435 seats in the U.S. House were up for re-election, although fewer than 90 were considered competitive. There are now 236 Republicans, 193 Democrats and six vacancies. So Democrats need to flip just two seats now held by the GOP in order to win control. All representatives are directly elected. "In reality, the exit polls just aren't precise enough to justify making distinctions between an electorate that's 15 percent black and, say, 13 percent black".
Democrats face a far more hard challenge in the Senate, where they are nearly exclusively on defense in rural states where Trump remains popular.
The party of a first-term president tends to lose seats in off-year elections and Trump's heated rhetoric and the acrimonious political climate has made even some Republicans jittery.
According to early predictions more than a dozen Republican-held seats have already flipped, while the Democrats appear to be holding onto their seats. Democrats in the Senate who appeared poised to win easy re-elections - like Tim Kaine in Virginia and Sherrod Brown of OH - did so.
As for Republicans retaining control of the Senate, she called it "a huge moment and victory for the president". If the Democrats control the House, they will be able to hinder Trump's ability to implement programs as he wishes.
The House can also initiate impeachment proceedings against the president, although it would need a two-thirds majority in the Senate to remove him from office.
The campaigns are canvassing neighborhoods and looking for people who still have not voted.
Voter turnout in the midterms is usually much lower than in the general elections, but this year seems to be a record year. "Because, man, they gave a lot of people a lot of reasons to be mad", he said. According to the Pew Research Institute the number of votes cast in Democratic primaries for the House were 84% higher in July than at the same point in the 2014 midterm primaries. Immigration is a top concern among Republican voters, and driving those issue-focused Trump supporters to the polls is key.