(CNN) - Maryland Gov. Martin O'Malley will endorse Cory Booker in New Jersey's special Senate election on Thursday, Democratic sources told CNN.
O'Malley, a former mayor of Baltimore, plans to cite the Newark mayor's efforts to reduce crime, attract businesses and improve education in his endorsement.
"We need more entrepreneurial, collaborative, results-driven leaders like Cory Booker in the U.S. Senate, not more politics as usual," O'Malley will say in a statement. "I plan to work hard to get him elected."
O'Malley will campaign with Booker later this summer.
Booker has three opponents for the Democratic nomination: Reps. Frank Pallone, Rep. Rush Holt, and state Assembly Speaker Sheila Oliver. New Jersey insiders are all but certain that the winner of the primary will capture the seat against token GOP opposition come election day.
While support from an out-of-state governor isn't likely to sway many New Jersey Democrats before the August primary or October special election, O'Malley's decision to takes sides in a contested Democratic primary is the latest example of his amped-up political activity as he lays groundwork for a potential presidential bid in 2016.
Since wrapping the Maryland legislative session in April, O'Malley has kept a busy schedule raising money for Democratic candidates on the ballot in 2013 and 2014.
He's lent his name to fundraisers for Massachusetts Senate candidate Ed Markey and Delaware Attorney General Beau Biden, the son of Vice President Joe Biden.
He's curried favor with Democrats in key presidential nominating states as well. On Wednesday, he raised money for Iowa Senate hopeful Bruce Braley at a reception in Maryland, an event attended by Iowa Sen. Tom Harkin, a key powerbroker and revered liberal in the Midwestern caucus state.
Earlier this year, O'Malley raised money for New Hampshire Sen. Jeanne Shaheen, South Carolina gubernatorial hopeful Vincent Sheheen, and Elizabeth Colbert-Busch, the Democrat who lost to Mark Sanford in May's special election in South Carolina's 1st Congressional District.
O'Malley is also scheduling trips to Pennsylvania, Ohio and Florida in the coming months to raise money for Democratic gubernatorial challengers there.