Retired Marine fighter pilot Amy McGrath defeated state Rep. Charles Booker in the race for Kentucky's Democratic Senate nomination, AP announced Tuesday.

Why it matters: McGrath was deemed an establishment favorite until Booker's progressive candidacy surged following national Black Lives Matter protests.

• Booker racked up a number of high-profile endorsements, including Rep. Alexandria Ocasio-Cortez (D-N.Y.), Sen. Bernie Sanders (I-Vt.), Sen. Elizabeth Warren (D-Mass.) and former HUD Secretary Julián Castro.
• Kentucky continues to deal with the fallout from the March police killing of Breonna Taylor in Louisville, and Booker has actively engaged with demonstrations calling for justice.

The big picture: McGrath garnered national attention in 2018 when she ran against Rep. Andy Barr (R) in Kentucky's 6th Congressional District, but she ultimately lost by about 10,000 votes.

• She will now take on incumbent Senate Majority Leader Mitch McConnell in November in what's likely to be an expensive race as fundraising machines for both parties gear up.
• However, McConnell is still the prohibitive favorite. Cook Political Report rates the race as "likely Republican."