Watch more of Nikole Killion's interview with Bernie Sanders and Alexandria Ocasio-Cortez on "CBS This Morning" on Monday.

Congresswoman Alexandria Ocasio-Cortez said she felt compelled to endorse Senator Bernie Sanders in the Democratic presidential primary because it was the "most authentic decision to let people know how I feel." The rising progressive star spoke to CBS News' Nikole Killion in an interview before the rally in Queens, New York, on Saturday where Ocasio-Cortez formally endorsed Sanders.

Ocasio-Cortez acknowledged that it was early to make an endorsement in the primary process, but she said her support was not motivated by political strategy. Saturday's rally is Sanders' first campaign event since returning to the trail after suffering from a heart attack October 2.

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"Some folks try to make these decisions by making political calculations and looking at political strategy but I think for me... it's coming from an authentic place," Ocasio-Cortez told Killion. She also reflected on her meteoric rise to politics, from a bartender to one of the best-known Democrats in the House.

"Last February, I was waitressing at a restaurant in downtown Manhattan and I didn't have health insurance and I wasn't being paid a living wage, and I was facing sexual harassment at work," Ocasio-Cortez said. "To think now that I'm on the other side of this as a member of Congress and understanding the pressures there are on inside to conform and to have seen them and experienced them firsthand — it's astounded me, frankly, that the senator has been there fighting for me long before I got to the halls of Congress and fighting for people like me."

Ocasio-Cortez was an organizer in Sanders' 2016 primary campaign. Sanders told Killion that it was "very significant" to have Ocasio-Cortez's endorsement, given her rising profile in the Democratic Party.

"It's very significant. Alexandria has been a political phenomenon. It is hard to believe that she has been in office less than one year and yet she has helped transform politics in America," Sanders said. Since entering office, Ocasio-Cortez has pushed for policies like "Medicare for All" and the Green New Deal.

"She has been an inspiration to millions of working people and young people throughout this country and her addition to this campaign is very, very significant. We're delighted to have her on board," Sanders said.