Booker is expected to win on Wednesday. If he does, he would enter the Senate at a pivotal moment.
The current president stumped for Rep. Ed Markey (D) Wednesday, while the 42nd president will campaign for him on Saturday. Meanwhile, Republican Gabriel Gomez is getting some much needed help over the airwaves.
Cory Booker is still the candidate to beat. But he faces a very different picture than he did last week.
The former governor seems to have taken to heart an old proverb: "When life gives you lemons, make lemonade."
The field of candidates includes Stephen Colbert's sister, a scandal-plagued former governor and the son of media mogul Ted Turner.
A run-down of who to keep an eye on in the days ahead, with a surprise cameo from Ben Affleck.
Republicans have begun a quiet campaign to promote another candidate for Secretary of State -- Sen. John Kerry (D-Mass.) -- which would lead to a special election.