Rep. Alexandria Ocasio-Cortez, D-N.Y., on Friday endorsed the reelection bid of Sen. Ed Markey, D-Mass., a champion of her "Green New Deal," against a potential primary challenge by Rep. Joe Kennedy III.

"Ed Markey is a proud and strong progressive champion for working families -- not just in Massachusetts but across the country," she said.

Markey, 73, joined the Senate in a 2013 special election before winning a full term the following year. The 38-year-old Kennedy, a grandson of late senator and attorney general Robert F. Kennedy, was first elected to the House in 2012.

The endorsement seemed to be personal for Ocasio-Cortez, who received early support from Markey for her ambitious proposals to address the specter of climate change.

"When I first got to Congress and we started to discuss big bold plans, a solution on the scale of the crisis, many members shied away," Ocasio-Cortez said in a video released on Friday.

"A lot of people said we can't do too much, we can't go too fast in order to pursue change for the American people," she added. "And Ed Markey was one of the few people that had the courage to stand up and take a chance, and take a chance on a freshman congresswoman."

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Markey was one of the sponsors of a resolution pushing the "Green New Deal" in the Senate. The Massachusetts senator also pushed cap-and-trade legislation early in former President Obama's administration.

Ocasio-Cortez's plan has come to symbolize progressives' aggressive agenda on the environment. She has faced pushback from members of her own party, like Sen. Dianne Feinstein, D-Calif., as well as sweeping attacks from Republicans who dubbed her a "socialist." Conservative groups have estimated the plan would cost trillions of dollars and inflict a heavy financial toll on American families.

Her endorsement seemed to fit with her record of challenging the Democratic establishment. While Kennedy has endorsed the freshman congresswoman's "Green New Deal," his family is also considered political royalty in Massachusetts.

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Ocasio-Cortez said that Markey's willingness to take a chance on her plan was "so emblematic" of who he was. "He's not just resting on his record of the past. He's aggressively pursuing an agenda for the future."

While Markey has enjoyed endorsements from Sen. Elizabeth Warren, D-Mass., and prominent liberal advocacy groups, he has trailed Kennedy in polling. A Suffolk University/Boston Globe poll earlier this month showed Markey with just 26 percent of primary voters' support, versus 35 percent for Kennedy.

Kennedy is expected to make a decision about challenging Markey by the end of September.