Comella is breaking from the governor she helped elevate into the national political limelight. Her decision, announced in an email interview with CNN's Jamie Gangel, comes the day after a top Jeb Bush aide said she was leaving the Republican Party.
Comella blasted Trump over his attack on the Muslim parents of an American soldier killed in combat, calling it emblematic of the rhetoric that has led her to reject her own party's nominee.
"Donald Trump has been a demagogue this whole time, preying on people's anxieties with loose information and salacious rhetoric, drumming up fear and hatred of the 'other,'" Comella said.
"Instead of trying anything remotely like unifying the country, we have a nominee who would rather pick fights because he views it as positive news coverage," she said. "It may make him media savvy, but it doesn't make him qualified or ready to be president."
Comella's decision is a dramatic departure from her former boss, whose image she helped shape on the national stage as one of his closest advisers and strategists while a long-serving top aide in Trenton, New Jersey.
Christie was among the first failed 2016 GOP candidates to endorse Trump, appearing alongside the Republican nominee at events and even lobbying to become his running mate.
But Comella -- like longtime Jeb Bush adviser Sally Bradshaw, who told CNN on Monday that she's left the GOP over Trump's nomination -- said party members can't stay silent amid Trump's inflammatory rhetoric.
"Instead of speaking out against instances of bigotry, racism and inflammatory rhetoric whether it's been against women, immigrants or Muslims, we made a calculus that it was better to say nothing at all in the interest of politics and winning elections. For me, if our party has a future, we have to change that trajectory and lead by example," she said.
Comella, like two other Christie communications aides, didn't return to Christie's office in New Jersey after his presidential campaign ended. The Republican governor is now without most of the advisers who guided him to two victories in the Democratic-leaning state.
The 35-year-old Comella has since launched her own consulting company.
Here's what she told CNN in a six-question email interview:
Why are you coming out against Donald Trump?
"As someone who has worked to further the Republican Party's principles for the last 15 years I believe that we are at a moment where silence isn't an option. We are here today in part because as a party in the past we have remained silent when things have made us uncomfortable. Instead of speaking out against instances of bigotry, racism and inflammatory rhetoric whether it's been against women, immigrants or Muslims, we made a calculus that it was better to say nothing at all in the interest of politics and winning elections. For me, if our party has a future, we have to change that trajectory and lead by example.
"We have to stop thinking that winning at any cost is more important than governing principles. It should be the job of the Republican Party's nominee to set a tone worthy of being the leader of the free world and not give into our worst instincts. I don't care if it's good politics or not."
Why now? Was there a tipping point?
"I've been contemplating whether to say anything publicly for awhile. When you are used to being behind the scenes and speaking for someone else it doesn't come naturally. For me, I think that it's a culmination of watching Donald Trump purposely play to our worst instincts and fanning those flames. We can't survive as a party if we don't try to elevate the conversation and lead. If those of us who believe that Donald Trump shouldn't be President don't say anything, we are just part of the same problem."
Who will you vote for and why?
"I'm voting for Hillary Clinton in November and I'm voting for her because I don't believe it's enough to say you aren't for Donald Trump. My mom and dad were Republicans, but they didn't always vote Republican. There are times when principle trumps (no pun intended) party and we have to be okay with acknowledging that.
"I can certainly complain that the choices aren't great and I wish there were better options. But there aren't. So I can either exist in the real world and make a decision based on my actual choices or pretend I am in a fantasy. I chose the real world and I would encourage other Republicans to do the same."
How did you react to Trump's recent comments about the parents of the Muslim-American soldier who spoke at the Democratic convention?
"I wish I could say I'm shocked, but I'm not. Donald Trump has been a demagogue this whole time, preying on people's anxieties with loose information and salacious rhetoric, drumming up fear and hatred of the 'other.' Instead of trying anything remotely like unifying the country, we have a nominee who would rather pick fights because he views it as positive news coverage. It may make him media savvy, but it doesn't make him qualified or ready to be president.
"The President of the United States is charged with making some of the toughest decisions any human being should have to confront, including sending men and women to war and potentially death. We can't have a President who doesn't understand the very human ramifications of those decisions and is unable to show humility and empathy in the face of grieving parents."
Unlike Sally Bradshaw, who is a longtime adviser to Jeb Bush who has also said he won't vote for Trump, your former boss, Gov. Chris Christie, has not only endorsed Donald Trump, but consistently defended Trump and lobbied to be his vice president. How do you think he will feel about your decision?
"I believe Chris Christie was the best person to be the nominee and unfortunately, that didn't happen. My decision is my own and I know from working with the Governor that he has the utmost respect for people expressing their own opinions."
How long have you been a Republican and what would you say to other Republicans about why you are doing this?
"I've been a Republican since I grew up listening to my parents talk politics at the kitchen table. Two people who came from working class families, never went to college and managed to send their two daughters to college as firsts in both families. They believed in a Republican Party that preaches that in this country there is opportunity for you no matter where you come from, who your parents are or what you grew up with. They believed in working hard, free trade, a government that delivers basic services well and is there when hard work alone isn't going to cut it. They didn't care what goes on inside the four walls of your home. Today, we have a nominee who doesn't represent any of those basic principles and he is just a culmination of our misdirection over the last few decades."