His vote will also reflect on Gov. Christie, a close friend and possible 2016 GOP presidential contender who handpicked Chiesa to replace the liberal Lautenberg.
In a 10-minute interview Tuesday, Chiesa declined to say where he will come down on the immigration package, but stressed his focus on border security, several times pointing to his previous work as a federal prosecutor and New Jersey attorney general.
"Much of the last 10 years I've spent as a prosecutor and as an attorney general, so the border security concerns are real to me," Chiesa said, citing worries about the drug trade, human trafficking, and terrorism. "We have to be sure that we're doing everything we can to keep that as secure as possible, to protect the people that already live here in a meaningful way."
The issue is fraught with policy and political implications. Democrats and some Republicans have argued that the GOP has no path to national victory unless it embraces immigration reform and reaches out to Hispanic voters.
But there is a fierce debate. Many conservatives argue that the bipartisan plan on the Senate floor amounts to "amnesty" for undocumented immigrants.
Chiesa said he is not thinking about the bill's political impact on Christie. "The governor asked me to do one thing - to come down and use my best judgment to make decisions that I felt were in the best interests of the people that I represent. That was it," Chiesa said.
He gave a glimpse of his judgment Tuesday, voting for two amendments to require tougher security provisions before undocumented immigrants can be given a path to legalized status. Both were supported only by Republicans and failed.
Each plan was opposed by fellow New Jersey Sen. Robert Menendez, a Democrat who is one of the prime advocates for a "pathway to citizenship."
Other plans to strengthen border controls are pending, most notably a proposal from Sen. John Cornyn (R., Texas) that Democrats warn could torpedo the bill. Chiesa said he had spoken with Cornyn but has not decided how he would vote on that plan.
On other topics, Chiesa said he was also still forming an opinion, stressing that he has only been in his job nine days, but he gave hints of where he stands.
Asked about government debt - an issue that could return this fall - he said he generally believes government has a "spending problem."
He called himself "pro-life" and said marriage is between a man and a woman.
On expanding background checks for gun purchases, he said he supported the Second Amendment and opposes "any additional undue burdens on legal gun ownership," but added, "We should be taking every step possible to keep guns out of the hands of people that shouldn't have them."
Chiesa, 47, has worked in the public eye but has not held elected office, he said, since being senior class president at Bound Brook High School.
Now he is part of the most exclusive lawmaking body in the country, if only until an October special election (he is not running). He does not yet have committee assignments.
He and his staff are working out of the trailer in the courtyard of the Russell Senate Office Building. The building's marble floors lead to a carpeted walkway into his office. There, printer paper with staff names on it is taped to cubicles. The only decoration is in Chiesa's office - an array of family pictures and one of him and Christie side by side.
Chiesa has a dozen staffers in Washington and two in New Jersey. (The normal complement for a New Jersey senator is 50 to 60.)
Chiesa has stayed with friends in Washington while he seeks a place to live during legislative sessions. "The getting settled part," he said, "has really been a continuing effort."
Contact Jonathan Tamari at email@example.com or follow on Twitter @JonathanTamari. Read his blog 'Capitol Inq' at www.inquirer.com/CapitolInq.