Mr. Booker, too, would have found a race against Mr. McConnell difficult. In choosing Ms. McGrath, however, Kentucky Democrats are hewing to a careful course, putting forth a well-funded political moderate with military credentials in a red state.
Mr. Booker, who ran as an outspoken progressive, argued that such an approach had been tried before and was doomed for failure. Winning the support of local newspapers and out-of-state liberal leaders like Senator Bernie Sanders of Vermont and Representative Alexandria Ocasio-Cortez of New York, Mr. Booker tapped into fury over the killings of Breonna Taylor and David McAtee to jolt what had been a quiet race conducted mostly under the radar until the last month.
Ms. Taylor was shot eight times after Louisville police officers entered her apartment with a battering ram. Mr. McAtee was shot at his barbecue stand in Louisville as the police and National Guard confronted curfew violators.
Mr. Booker conceded the race Tuesday evening and urged Democrats to “dedicate to the work of beating Mitch,” even as he noted that some voters had trouble casting ballots during the pandemic and raised questions about some absentee ballots not being counted.
In his statement, Mr. Booker barely mentioned Ms. McGrath — except to say the race wasn’t “about me and Amy” — but he implicitly swiped at her campaign. “We’ve proven you don’t have to pretend to be a Republican to run as a Democrat in Kentucky, and that people want big, bold solutions,” he said.
Establishment-aligned national Democrats, led by Senator Chuck Schumer of New York, had effectively sought to coronae Ms. McGrath last year. By virtue of the large fund-raising list she built in her failed 2018 House race, and the contempt Democratic donors have for Mr. McConnell, they viewed her as someone who could run competitively and perhaps force Republicans to divert money to Kentucky.
She will still have ample cash for her race against Mr. McConnell, who is seeking a seventh term, but her uneven performance as a candidate, first in 2018 and again in this primary, has raised doubts about how strong of a campaign she will run in the general election.