According to a Booker adviser, the mayor's campaign made the two high-profile hires this week. 

DeMicco is a Booker veteran, having aided the 2006 campaign that brought him to city hall. He also  managed the campaigns of Sens. Bob MenendezRobert (Bob) MenendezPoll: Menendez has 17-point lead over GOP challenger Russian attacks on America require bipartisan response from Congress Justice Dept intends to re-try Menendez in corruption case MORE (D) and Lautenberg, as well as former Gov. Jon Corzine (D), among others.

Though Booker has not yet publicly confirmed his intentions to run, he has already begun collecting signatures to join the primary ballot and the source said he's planning his campaign rollout for Saturday, when he expects to unveil some "big-name" endorsements.

"We feel good. I met with the mayor tonight and spent some time going through a lot of things. Endorsements are starting to come, we're looking at slogans, just trying to figure everything out," the source said.

Lautenberg's death early Monday morning came as a surprise to Booker, and he has spent much of the week working to get his staff back to New Jersey and ready to operate.

He'll face Rep. Rush Holt (D), who has already announced his intentions to run, and Rep. Frank Pallone (D), who is expected to announce soon, in the Democratic primary on Aug. 13.

Booker is favored to win the primary, and the eventual Democratic nominee is likely to take the seat in the general election, on Oct. 13.

The adviser said that the condensed timeframe of the special election has increased the pressure on Booker's campaign somewhat, but that Booker and his staff aren't concerned about their chances going forward.

"It's a consolidated timeframe, so we're now putting all the pieces in place, running the drill. We're feeling very confident, if we do what we're supposed to do," the adviser said.

On Thursday, New Jersey Gov. Chris Christie (R) appointed state Attorney General Jeff Chiesa to temporarily fill the seat until the special.