In 2018, she became the first Democrat in 50 years to win Virginia’s Seventh Congressional District, to the north of Richmond. Representative Hakeem Jeffries, Democrat of New York and the minority leader, chose her for the response, people familiar with his thinking said, because he believes that her gubernatorial campaign, which focused on affordability and prosecuting the case against Mr. Trump, was a model for how Democrats can win races across the country in November.