Newark Mayor Cory Booker walks in Collingswood, N.J., during a campaign stop on in late July.(AP Photo/Geoff Mulvihill)

Maryland Gov. Martin O’Malley (D) called for greater federal investment in the nation’s cities as he campaigned in New Jersey on Thursday for the election of Newark Mayor Cory Booker (D) to the U.S. Senate.

“We need an urban policy, we need to have a city policy,” O’Malley, a former mayor of Baltimore, said during an appearance at a public housing complex in Trenton, the first of four advertised stops in the Garden State on Thursday on behalf of Booker.

O’Malley said Booker represents “a rare and golden opportunity to elect a mayor” to Congress, which he said needs to “reinvest in the heart of our cities.”

“There is not the city perspective we need in the United States Senate, and Cory is going to bring that, said O’Malley, who endorsed Booker in June.

O’Malley stood in for Booker at the event in Trenton and two other events in Paterson, including one at an Irish tavern. Later, after a debate that included Booker and three other Democrats vying for the party’s Senate nomination in a special election, O’Malley and Booker appeared together in Newark.

Booker, who was preparing to launch a bus tour, said that when he was running for mayor in 2006, then-Mayor O’Malley was a role model.

“Gov. O’Malley was the guy we looked to,” Booker said. “We went down there and studied the way O’Malley managed his city.”

Among the Baltimore initiatives that Booker embraced was CitiStat, a program that seeks to hold government agencies accountable through a bevy of statistical measures of performance.

O’Malley, who is weighing a 2016 presidential bid, said he plans to return to New Jersey in coming months to campaign for the state’s Democratic gubernatorial candidate, Barbara Buono, in a contest this fall against Gov. Chris Christie (R).