Bradshaw told CNN in an email that the GOP is "at a crossroads and have nominated a total narcissist — a misogynist — a bigot."
"This is a time when country has to take priority over political parties. Donald Trump cannot be elected president," Bradshaw wrote.
"This election cycle is a test," she added in her email. "As much as I don't want another four years of Obama's policies, I can't look my children in the eye and tell them I voted for Donald Trump. I can't tell them to love their neighbor and treat others the way they wanted to be treated, and then vote for Donald Trump. I won't do it."
Bradshaw was a top adviser to Jeb Bush's failed presidential bid, working especially on hiring staff and crafting his overall message. She's now essentially left the rough and tumble of politics and opened a bookstore in Tallahassee.
After the 2012 election, she was drafted by top RNC leaders to help co-write an after-action report to assess how the party suffered yet another White House loss. The report called for less of a focus on social issues and for party members to adopt a softer tone when discussing immigration and other issues of importance to minorities.
Widely heralded after its publication, the report has been essentially tossed aside in the years since and was widely dismissed by several of the party's presidential candidates this past year.
Bradshaw did not return requests for further comment.
Over the weekend, Jeb Bush was among the handful of senior Republicans to weigh in on Trump's latest feud with Khizr and Ghazala Khan, the parents of Army Capt. Humayun Khan, was killed by a car bomber in 2004.