A liberal backed by Senator Bernie Sanders pulled off an upset in the Democratic primary for Florida governor on Tuesday, setting up a November showdown between the party's progressive wing and a Republican aligned with President Donald Trump.
Andrew Gillum, the mayor of Tallahassee, beat moderate Gwen Graham, a former US representative and daughter of a prominent Florida politician, after running as an unabashed progressive who backed "Medicare for all," impeaching Trump and standing up to the National Rifle Association.
Gillum, 39, will square off in November against Republican US Representative Ron DeSantis, a conservative who won his primary by touting his closeness to Trump, in one of the country's top governor's races.
The battle between progressives and conservative Trump Republicans will be closely watched by both parties for clues about the mood of voters and messaging ahead of 2020, when Trump could be seeking re-election against a liberal Democrat.
The Florida contest came on the last big day of state nominating contests before the Nov.6 elections, when Democrats will try to pick up 23 seats in the US.
House of Representatives and two seats in the Senate to gain majorities and slam the brakes on Trump's legislative agenda.
In Arizona, Republicans chose US Representative Martha McSally, an establishment favorite, NBC News projected, in a three-way Senate primary that became a battle to prove who was most loyal to Trump.
Businessman Kevin Stitt won the Republican nomination for governor in Oklahoma in a primary runoff race against the former Oklahoma City Mayor Mick Cornett.
Stitt had aligned himself with Trump and questioned Cornett's allegiance to the president.
However, the biggest surprise came in Florida, where Gillum trailed Graham in the polls through much of the race but surged in the final stages with the backing of Sanders and high-profile liberal donors like George Soros and Tom Steyer.
Gillum, who would be the political battleground state's first black governor, emphasized his background as the son of a bus driver and construction worker and pledged to galvanize younger and minority voters who often sit out midterm elections.
"We have shown the rest of the country that we can be the David in the situation where there is a Goliath," he told supporters after his victory.
"That you can be the non-millionaire, you can come from a working class family, and you can make your way to the top."
The conservative DeSantis easily won the Republican primary by highlighting his enthusiastic loyalty to Trump.
DeSantis, who was endorsed by Trump, beat state Agriculture Commissioner Adam Putnam.
"I am not always the most popular guy in DC, but I did have support from someone in Washington. If you walk down Pennsylvania Avenue, he lives in the White House with the pillars in front of it," DeSantis told supporters after his win, noting he had spoken to Trump.
Florida will also host one of the country's top US Senate races between term-limited Republican Governor Rick Scott, who won the Senate nomination against token opposition, and incumbent Democrat Bill Nelson.
Nelson ran unopposed for the nomination.
In Arizona, which Trump won by 4 percentage points in 2016, former fighter pilot McSally had led in opinion polls over former state Senator Kelli Ward and controversial former Maricopa County Sheriff Joe Arpaio in the Senate nominating battle.
The Arizona contest to replace the retiring Jeff Flake is considered one of the two top takeover opportunities for Democrats, along with Nevada, and could be critical to the balance of power in the Senate in November.
McSally is seen as a stronger general election candidate than either Ward or Arpaio, both hard-line conservatives.
McSally has already launched advertising aimed at her Democratic opponent in November, US Representative Kyrsten Sinema, who easily won nomination against token opposition.
Only five states remain to pick candidates after Tuesday's primaries before full attention turns to the November election, when all 435 House seats and 35 of the 100 Senate seats will be at stake.