Former fighter pilot Amy McGrath wins battle to face Mitch McConnell for Kentucky Senate seat in November

Senate Majority Leader Mitch McConnell will face retired US fighter pilot Amy McGrath in Kentucky's US Senate race this autumn, after Ms McGrath beat back a late primary surge by progressive state representative Charles Booker.

The Associated Press declared Ms McGrath, who has raised more than $40m so far this cycle, the victor of the Democratic primary on Tuesday, a full week after Election Day in the Bluegrass State, as several precincts continued to count absentee and mail-in ballots.

As of 12:45 p.m. on the East Coast, Ms McGrath had captured 45.1 per cent of the vote compared to Mr Booker's 43 per cent.

"I'm humbled that Kentucky Democrats have nominated me to take on Mitch McConnell in the general election and can't wait to get started in sending him into retirement and finally draining the toxic Washington political swamp that he built," Ms McGrath said in a statement after the AP's announcement she had won the nomination.

Ms McGrath has nearly $20m in cash on hand to spend on her general election race against Mr McConnnell, the Kentucky GOP political machine who has been instrumental in reshaping the federal judiciary in his conservative image during the Trump administration and was a thorn in the side of former Democratic president Barack Obama.

While Ms McGrath was the chosen Democratic candidate of Senate Minority Leader Chuck Schumer and has proven to be a prolific fundraiser, capitalising on nationwide liberal disdain for Mr McConnell, she is considered a long shot to defeat the majority leader.

Inside Elections with Nathan L Gonzales rates the race Solid Republican. The Cook Political Report rates it Likely Republican.

Mr Booker, who ran on a progressive platform espousing "Medicare for All" and a "Green New Deal," made a late surge in the Democratic primary race after the deaths in police custody of Breonna Taylor in Louisville and George Floyd in Minneapolis.

He had earned the endorsements of Independent Senator Bernie Sanders of Vermont and Democratic Congresswoman Alexandria Ocasio-Cortez of New York, two progressive lynchpins, and even received the backing of the Louisville Courier-Journal and the Lexington Herald-Leader, the two most widely circulated newspapers in the state.

Ms McGrath acknowledged on Tuesday that Mr Booker had "tapped into and amplified the energy and anger of so many who are fed-up with the status quo and are rightfully demanding long overdue action and accountability from our government and institutions."

Mr Booker beat Ms McGrath in Kentucky's two most populous counties, indicating he had developed a groundswell of support in urban centres in the commonwealth.

But Ms McGrath largely carried the rural parts of Kentucky that Democratic operatives also see as key to winning the general election.

"There can be no removal of Mitch McConnell without unity. We must unify our Democratic family to make that happen, including those who didn't vote for me in the primary," Ms McGrath said.

"I intend, immediately, to start the dialogue necessary to bring us all together in our common cause for the general election. ... The differences that separate Democrats are nothing compared to the chasm that exists between us and the politics and actions of Mitch McConnell. He's destroyed our institutions for far too long," she said.

While Ms McGrath faces an uphill battle to unseat Mr McConnell, who has represented Kentucky in the Senate since 1985 and led the Senate GOP since 2007, Democrats have notched some recent successes in the state.

Democrat Andy Beshear defeated Republican incumbent Matt Bevin by roughly 5,000 votes in the race for governor last year.

Mr McConnell's re-election campaign welcomed Ms McGrath to the general election race with a tweet trolling her for an innocuous verbal gaffe in an interview with CNN's Jake Tapper in which she tells the host, "Great to have you."

Mr McConnell has painted Ms McGrath as the "extreme" choice of the liberal establishment, hitting her on her stances on abortion and health care.

Ms McGrath has "no idea what matters most to Kentuckians" and "does not represent Kentucky values," Mr McConnell's campaign said in a press release on Tuesday.