And as Americans gear up for the November 6 vote, there are several candidates looking to make history again.
From the first expected Muslim congresswomen to the first expected openly gay governor, here’s who to look out for:
Tlaib, a Palestinian American, is running for Michigan’s 13th Congressional District without a competitor.
Omar, who arrived in the US at the age of 14 after fleeing civil war in Somalia, is contesting Minnesota’s 5th District.
Omar would also be the first Somali American to serve in the US Congress.
Alexandria Ocasio-Cortez beat 10-term incumbent Joe Crowley in the Democratic primary for New York’s 14th District and if she, as expected, wins in the midterm elections she will make history as the youngest woman in history to join Congress.
Born to a father from South Bronx and a mother from Puerto Rico, Ocasio-Cortez was an organiser for the 2016 Bernie Sanders presidential campaign.
A member of the Georgia House of Representatives since 2007, Stacey Abrams has already made history as the first black woman to win a nomination to run as governor by a major party, but she’s hoping to go a step forward by winning the state’s gubernatorial election.
She’s running close behind Republican candidate Brian Kemp, with polls putting her within two percentage points of her rival.
The race has been marred by allegations of voter suppression. Kemp, Georgia’s current secretary of state, is currently holding up 53,000 voter registration applications, most of them belonging to African Americans. He says he’s complying with the states “exact match” ID law, but Abrams maintains her opponent “has disproportionately purged voters of colour, stopped voters of colour, arrested voters of colour”.
If Deb Haaland can hang on to her lead in New Mexico’s 1st District House race, she will become the first Native American woman elected to Congress.
Haaland, a member of the Pueblo of Laguna tribe, says she will prioritise climate change, as well as a number of other progressive issues, such as Medicare-for-all and debt-free education.
With a net worth of close to $400m, Democrat Jared Polis is already one of the richest members of the House of Representatives but in entering the Colorado gubernatorial contest, he could become the first openly gay governor of a state.
Opinion polls give him a comfortable seven-point lead over his Republican rival, Walker Stapleton.
Democrat Ayanna Pressley surprised many when she upset 10-term incumbent Michael Capuano during Massachusetts’s 7th Congressional District primary.
She is running uncontested on November 6, meaning she is set to become the state’s first black congresswoman.
In a state with a Hispanic population of close to 40 percent, Veronica Escobar and Sylvia Garcia are hoping to become the first women of Latin American origin to represent Texas in the House of Representatives.
Escobar is running in Texas’s 16th District, while Garcia is running in the state’s 29th District. Both are Democratic strongholds and it looks likely they will on November 6.
Christine Hallquist made history in August when she won the Vermont Democratic gubernatorial nomination for 2018, becoming the first transgender woman to get on to a major party ticket for governor.
The former IBM engineer faces an uphill task from there, however, with polls giving Republican rival Phil Scott a double-digit lead.
If Tallahassee Mayor Andrew Gillum can best Republican US Representative Ron DeSantis on November 6, he will become the state’s first black governor. The 39-year-old already made history during the primary when he became the first black major party nominee for governor in Florida.
The latest opinion polls showed Gillum with a slight lead over his opponent. The progressive candidate, who advocates for Medicare-for-all and abolishing Immigration and Customs Enforcement (ICE), has been a frequent target of President Donald Trump.
Women won a record number of primary races in Nevada’s primary. Female candidates are favoured to control 27 seats after the November election, but they would still need five to control the majority, according to the Reno Gazette. The newspaper noted, however, there are a number of tight races in which women could pick up the seats needed.