CINCINNATI — They stormed the stage together wearing similarly colored clothes — hues that almost perfectly matched the bold blue of Hillary Clinton’s presidential campaign logo. With a “Stronger Together” sign hanging in the background and a Katy Perry pop song blaring from the speakers, they cheered each other on like old pals, cracking jokes about Donald J. Trump and pointing with enthusiasm at a young supporter who waved a placard that read “Girl Power.”
Senator Elizabeth Warren of Massachusetts, a towering political figure among today’s liberal Democrats, brought her energy, folksy appeal and populist roar to a candidate not known for energizing crowds.
For Ms. Warren, the joint event with Mrs. Clinton here on Monday, the first time the two Democrats campaigned onstage together, was a moment for her to elevate her profile as the liberal voice of the party and a favorite to be vice president.
For Mrs. Clinton, it was a chance to woo the party’s liberal wing and convince economically hard-hit voters that she, too, is a populist champion running for president to improve their lives.
“I got into this race because I wanted to even the odds for people who have the odds stacked against them,” Mrs. Clinton told the crowd. “To build an economy that works for everyone, not just those at the top, we have got to go big and we have got to go bold.”
Mrs. Clinton stood onstage grinning and nodding, her hands clasped calmly at her waist, as Ms. Warren eviscerated Mr. Trump in remarks that lasted roughly half as long as Mrs. Clinton’s half-hour address.
Ms. Warren told an electrified crowd of roughly 2,600 gathered in the grand corridor of the Cincinnati Museum Center, under murals of factory and farmworkers, that the presumptive Republican nominee would “crush you into the dirt to get whatever he wants.”
And when Ms. Warren, a onetime critic of Mrs. Clinton, turned from the lectern to face the presumptive Democratic nominee, declaring that she “has never backed down” from fighting for the middle class, Mrs. Clinton flashed a wide, satisfied smile, appearing to let out a sigh of relief that she had the liberal senator from Massachusetts in her corner. She mouthed two simple words to her supercharged surrogate: “Thank you.”
The event was the culmination of warming relations between Mrs. Clinton and Ms. Warren, who has criticized the financial policies of the Bill Clinton era. Before she was a senator, Ms. Warren turned her ire on Mrs. Clinton, then a New York senator, for shifting her position to support bankruptcy legislation that would have made it more difficult for families to get debt relief.
