A CBS News reporter asked Rep. Alexandria Ocasio-Cortez, D-N.Y., why she endorsed “old white guy” Sen. Bernie Sanders, I-Vt.

CBS News correspondent Nikole Killion spoke with Sanders and Ocasio-Cortez for a wide-ranging interview that aired Monday on “CBS This Morning.”

“As a woman of color, why back an old white guy? And is this the future of the party?” Killion asked Ocasio-Cortez.

Ocasio-Cortez defended her decision.

“I’m actually very excited about this partnership because it shows what we have to do in our country,” Ocasio-Cortez responded. “We have to come together across race, across gender, across generations.”

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Ocasio-Cortez told Killion that she first offered her endorsement to Sanders when he was in the hospital after recent heart surgery because his illness was a “gut check.”

“Neither me, nor the senator, can do this by ourselves,” Ocasio-Cortez said.

Killion was also criticized over another question she asked during the same interview when the CBS reporter pondered if Sanders would select the 30-year-old New Yorker as his running mate if he emerges as the nominee.

“I think I’m too young for that,” she said while laughing.

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Sanders chuckled and said: “There you go, she answered it.”

Ocasio-Cortez, who has quickly become one of the most prominent left-wing House lawmakers since taking office in January, backed Sanders formally at the rally in Long Island City, New York on Saturday. She credited Sanders with having inspired her to embark on her own long-shot political bid, in which she ousted longtime Rep. Joe Crowley last year.

Fox News’ Adam Shaw contributed to this report.