O'Malley endorses Van Hollen in Senate race
© Greg Nash

Former Democratic presidential candidate Martin O'Malley is throwing his support behind Rep. Chris Van Hollen, a day before Tuesday's Democratic Senate primary in Maryland. 

"I stood with Barbara MikulskiBarbara Ann MikulskiBottom line How the US can accelerate progress on gender equity Former Md. senator Paul Sarbanes dies at 87 MORE in her historic campaign for U.S. Senate in 1986, and I’m standing with Chris tomorrow on election day," O'Malley, who worked on the retiring Democratic senator's campaign 30 years ago, wrote to supporters on Monday.
 
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"I hope you will join me in voting for a progressive who will get things done for the state we love," O'Malley added.
 
Van Hollen held a 6-point lead over Democratic primary rival Rep. Donna Edwards in a poll released earlier this month.
 
Van Hollen has been seen as the establishment favorite in the heated primary race, securing Senate Minority Leader Harry ReidHarry Mason ReidWhite House races clock to beat GOP attacks Harry Reid reacts to Boehner book excerpt: 'We didn't mince words' The Memo: Biden seeks a secret weapon — GOP voters MORE's (D-Nev.) endorsement early last year, while Edwards has been backed by several high-profile progressive groups and figures.
 
O'Malley, the former governor of the state who ran unsuccessfully for the 2016 Democratic presidential nomination, praised Van Hollen's record on gun control, education and environmental issues.
 
"In my time serving on the Baltimore City Council, as Mayor of Baltimore, and as Governor, Chris was a reliable, progressive partner in the General Assembly and in Congress," O'Malley wrote.
 
"At this critically important time for Maryland and our country, we need a progressive U.S. Senator who is able to deliver results for our great state and to move the nation forward," O'Malley added. "That progressive is Chris Van Hollen, and I’m urging you to support him in the primary tomorrow."
 
O'Malley has declined to weigh in on another Democratic primary that Maryland voters will vote on Tuesday: the presidential race.