WASHINGTON — Now that Senator Bernie Sanders is all but out of the race, Democrats can unite to take aim at Donald J. Trump. Their new sledgehammer is Senator Elizabeth Warren.

In her day job, Ms. Warren cuts an imperious swath through the Capitol, striding down hallways, her jewel-toned jacket swaying behind her, refusing to speak to or even make eye contact with reporters. Small talk with elevator operators and other staff? Not her style. And the Democrat from Massachusetts is rarely front and center pushing major legislation.

But beyond Mr. Sanders, no one captivates the aggrieved, angry left the way Ms. Warren does.

“What she is doing right now, focusing on the outrageousness of Donald Trump is really important,” said Senator Tammy Baldwin, Democrat of Wisconsin. “In the universal sense I am always saying, ‘Go, Elizabeth, go!’”

Ms. Warren officially endorsed Hillary Clinton on Thursday. “I’m ready to jump in this fight and make sure that Hillary Clinton is the next president of the United States and be sure that Donald Trump gets nowhere near the White House,” Ms. Warren told The Boston Globe.