[Elizabeth Warren has dropped out of the 2020 democratic presidential race.]

ARLINGTON, Va. — Senator Elizabeth Warren of Massachusetts said Thursday that Michael R. Bloomberg should not be the Democratic presidential nominee because of newly surfaced comments he made 12 years ago in which he said the end of a discriminatory housing practice had helped contribute to the 2008 financial crisis.

Ms. Warren’s comments, made at an event here in Northern Virginia, were a strikingly direct broadside against a rival as she tries to reignite enthusiasm for her campaign after her fourth-place finish in New Hampshire this week.

“A video just came out yesterday in which Michael Bloomberg is saying, in effect, that the 2008 financial crash was caused because the banks weren’t permitted to discriminate against black and brown people,” Ms. Warren told a crowd of supporters packed into a high school gymnasium. “That crisis would not have been averted if the banks had been able to be bigger racists. And anyone who thinks that should not be the leader of our party.”

The comments were a strategic shift for the Massachusetts senator, who has typically tried to stay above the attacks and counterattacks traded by many of her rivals. On Tuesday evening in New Hampshire, she had criticized the aggression shown by some of the other candidates, urging them to forgo “harsh tactics.”