Sen. Elizabeth Warren is throwing her "full support" behind her "great partner in the United States Senate, Ed Markey."

In a 90-second YouTube video, Warren called her fellow Democratic senator a "true progressive," saying Massachusetts needs Markey in the Senate "now more than ever." Warren's endorsement comes amid reports that Congressman Joe Kennedy III is considering a primary challenge against Markey in 2020.

Warren cited Markey's work on climate change, universal health care, addressing the nation's opioid epidemic and strengthening national gun laws.

"On the big issues facing Massachusetts, Ed is our greatest champion in the Senate," Warren said.

In a tweet Monday afternoon, Sen. Markey said of Warren, "I am honored to have her strong support for my reelection."

Labor attorney Shannon Liss-Riordan and businessman Steve Pemberton have already announced they will challenge Markey for the Senate seat.

Markey, a Malden Democrat, was first elected to the Senate in 2013 after first being elected to the U.S. House of Representatives in 1976.