While Christie's decisions resolved one pressing question, it left open another: Who will represent the GOP in the fast-approaching elections?
Many of the names floated this week have publicly and privately backed away from a race that looks daunting for Republicans.
So far, conservative stalwart Steve Lonegan, a former Bogota mayor who has twice run for governor but fallen short in primaries, is the only Republican in the race.
Hours before Chiesa was appointed, U.S. Rep. Rush Holt, who represents parts of four counties in the central part of the state, became the first Democrat to publicly enter the contest, announcing his decision in an e-mail to supporters and attempting to claim the mantle of the heir to Lautenberg's liberal legacy.
"I believe I am the best candidate to continue the passionate advocacy for progressive values that Sen. Lautenberg exemplified," Holt wrote.
At least two other Democrats are expected to run. A Democratic source has said U.S. Rep. Frank Pallone, whose district includes Shore towns, will enter the race, and Newark Mayor Cory Booker also is collecting signatures needed to run, his campaign confirmed. With a Monday filing deadline, formal announcements are expected soon.
Chiesa in retrospect made sense to political watchers: He is a Christie loyalist who has nonetheless been publicly praised by Democratic legislators.
The state's top elected Democrat, Senate President Stephen Sweeney (D., Gloucester), called Chiesa "capable" Thursday but said Lautenberg should have been replaced with another Democrat.
Christie's announcement in Trenton came at the same time as an honor guard in Washington carried Lautenberg's casket into the Capitol for a final farewell.
First hired by Christie at a law firm in 1991, Chiesa later joined Christie in the U.S. Attorney's Office and led public corruption cases, including the prosecution of former Senate President John Lynch. He became Christie's chief counsel in the governor's office and was then appointed as the state's top law enforcement official.
"There's very few people in my life that I know better than Jeff," Christie said. "I have enormous respect and admiration for him, and his integrity and his honesty and his ability."
Chiesa was joined by his wife, Jenny, and their two children, who blinked in the bright TV camera lights. He repeatedly referred to the opportunities Christie has given him.
"The governor has given me some extraordinary chances to serve in public life," Chiesa said. "It really is extraordinary to me that I'm standing here today, again, with his confidence and support."
The governor went to Chiesa's house in Branchburg, in central New Jersey, on Monday night to offer the job. The next morning he received a text.
"I'm in," Chiesa wrote.
Christie said he would appoint an acting attorney general on Monday, the day Chiesa will be sworn in as senator.
Despite their friendship, Christie said Chiesa won't be his personal representative in Washington.
"If he calls me and says, 'There's a vote for cloture on the following bill, what should I do?', I'd hang up," Christie said.
Chiesa called himself a conservative Republican - "generally speaking" - but refused to give any hints about how he'll vote.
On immigration, which may be his first major vote, he said only that he was concerned about border security due to his experience dealing with such issues as an assistant U.S. attorney.
The Senate also is facing a pressing debate on student loan rates, and in the fall may hit another fiscal deadline, when the Obama administration hits the debt ceiling.
The governor's office highlighted Chiesa's work combating human trafficking, indicting child pornography offenders, and implementing the "most sweeping" gun-buyback program in state history.
As the governor's chief counsel, he was cited for negotiating some of the governor's most significant legislation.
Christie on Thursday also continued to defend his decision to hold the special Senate election in October, instead of 20 days later on the day he runs for office. It has been widely speculated that Christie did this - at a cost of $11.9 million - to increase his own reelection chances by keeping a popular Democratic candidate for Senate, such as Booker, off the same ballot.
Christie again rebutted this Thursday, pointing to a passage from the 1947 state constitutional convention in which the framers said state and federal elections should be held on different days.
And he said a 2009 quote highlighted by The Daily Show on Wednesday - in which Christie said a "responsible" governor wouldn't hold an expensive special election for the Senate - was taken out of context. He said he was specifically referring to former Gov. Jon S. Corzine, who made an appointment to fill his own seat in the Senate.
"No responsible governor would spend $10 million on a special election to replace themselves, that was the context of the statement," he said.
Holt, from Hopewell, Mercer County, has been in the House for 14 years. He was once the assistant director of the Princeton Plasma Physical Laboratory, leading to one of New Jersey's most recognizable political bumper stickers: "My Congressman IS a Rocket Scientist."
His father was a one-term senator from West Virginia, serving from 1935 to 1941.
Jeffrey S. Chiesa
Residence: Branchburg, N.J.
Political party: Republican.
Latest appointment: He was appointed by Gov. Christie as a U.S. senator, effective Monday, filling seat of the late U.S. Sen. Frank R. Lautenberg until the winner of an Oct. 16 special election takes office. He will not run for election.
Role in Christie administration: He has been state attorney general since Jan. 10, 2012. Before that he was the governor's chief counsel, 2010-11, and executive director of the governor's transition team following Christie's 2009 election.
Federal prosecutor: He served under then-U.S. Attorney Christie, 2002-09.
Private practice: A partner at the firm of Wolf & Samson and earlier at the firm of Dughi & Hewit, where Christie also practiced.
Education: A law degree from Catholic University of America, 1990; bachelor's degree from University of Notre Dame, 1987.
Family: wife, Jenny; two children.
Quote: "I've only had these chances because of the governor. I don't kid myself."
SOURCE: Associated Press
Contact Matt Katz at 609-217-8355, firstname.lastname@example.org, or follow @mattkatz00 on Twitter. Read his blog, "Christie Chronicles," at www.philly.com/christiechronicles.