US Democrats have made gains in state elections, in what is being seen as a blow to President Donald Trump.
Democrat Andy Beshear claimed victory in Kentucky's governor vote, after a tight race in the conservative-leaning state.
Meanwhile, Democrats seized full control of the legislature in Virginia for the first time in over 20 years.
The results are being viewed as a gauge of the political mood ahead of next year's presidential election.
However, Republicans held on to power in the Mississippi governor vote, following a closely-fought race.
US state governors head the executive branch in state governments.
In Kentucky, Mr Beshear claimed victory over incumbent Republican governor Matt Bevin after final results gave him a lead of 0.4%.
Mr Bevin, 52, says he will not concede, citing unspecified "irregularities".
However, Mr Beshear, a 41-year-old attorney general whose father was a former governor of the state, said: "We will be ready for that first day in office and I look forward to it."
The loss will be seen as a setback for Mr Trump, who attempted to galvanise support for Mr Bevin at a campaign rally in Kentucky on Monday night.
In a speech to thousands of supporters, Mr Trump said a loss for Mr Bevin would be characterised as "the greatest defeat in the history of the world" by his critics.
Mr Trump, who won the state of Kentucky in the 2016 presidential election, said Mr Beshear was "too extreme and too dangerous" to govern the state.
However polls showed Mr Bevin was one of the least popular governors in the country, following high-profile battles with unions and teachers.
Despite losing the governor's race, Republican candidates claimed victory in five other votes in Kentucky, including a poll for the state's Attorney General.
Meanwhile, in Virginia, Democrats overturned Republican majorities in both chambers of the state legislature.
The election of Danica Roem, the first openly transgender person to serve in the House, and Ghazala Hashmi, who will be the first Muslim woman in the Senate, were among the Democrat's notable victories in the state.
Virginia also saw Juli Briskman – who gained US media attention in 2017 after she lost her job for making an obscene gesture at Mr Trump's motorcade – elected as a district representative in Loudoun County.
Ahead of the vote, Democratic presidential hopefuls – including frontrunners Joe Biden and Elizabeth Warren – had campaigned with local candidates.
Kentucky suburbs defy Trump
Anthony Zurcher, BBC's North America correspondent
Republican Matt Bevin was a Donald Trump-style candidate a year before Donald Trump won the presidency.
Once in office, Bevin governed a lot like Trump, as well. Despite sinking popularity in opinion polls, he contended that he would win comfortable re-election.
He didn't. Bevin's strength in the rural parts of the state weren't enough to overcome Beshear's margins in the cities and – of particular concern to Republicans – the kind of suburban areas that also were key to many Democratic wins in 2018.
Trump himself threw his support behind Bevin in the campaign's closing days, holding a rally in Louisville on Monday Read More – Source