She described the 2012 Republican presidential candidate as “nothing but awful”, revealing divisions in Trump’s transition team about who should be part of the new administration.
On Sunday, Ms Conway told TV reporters: “People feel betrayed to think that Gov. Romney, who went out of his way to question the character and the intellect and the integrity of Donald Trump, now our president-elect, would be given the most significant cabinet post of all”.
She continued her attacks over social media, tweeting: “The volume and intensity of grassroots resistance to Romney is breathtaking”, adding to pressure on Trump to drop the former Governor of Massachusetts from the running to take one of the top White House positions.
Ms Conway, who managed Trump’s winning election campaign, resorted to a Twitter crusade against Romney after she claimed she had tried speaking to Trump privately to voice her concerns.
MSNBC reported the President-elect was left “furious” by the comments, with sources close to the present allegedly saying: “Kellyanne went rogue at Donald Trump”s expense at the worst possible time.
“Instead of driving Donald Trump”s message, she”s pushing her own agenda.”
Ms Conway is not alone in her concerns over Romney’s potential appointment – former Arkansas Governor Mike Huckabee and former House Speak Newt Gingrich, two high-profile Trump loyalists, have expressed fears about the impact Romney’s potential appointment could have on the Republican Party.
Last week, Huckabee said: “It’s not about that I don’t care for Mitt personally, but I’m still very unhappy that Mitt did everything he could to derail Donald Trump.
“He didn’t just go after him from a standpoint of saying I disagree with his policy on immigration or I disagree with his policy on taxes.”
He added: “He attacked him on a personal level about his character, integrity, his honour.”
Gingrich has also attacked Romney, claiming he felt the 2012 GOP nominee was Trump’s “most vicious and most explicit opponent all through the campaign on the Republican side”.
These high-profile criticisms of Romney could put pressure on the President-elect to opt for former New York City mayor Rudy Giuliani as his new Secretary of State, who appears to be the other major contender for the role.
However, Trump is reportedly unhappy that top-ranking Republicans are publicly criticising contenders for some of the most important roles in his government.
In his Thanksgiving video message, Trump called for unity in America following one of the most divisive presidential campaigns in US history.
Should Romney be elected the Trump’s new US Secretary of State, the appointment would mark an astounding turnaround in the relationship between the two Republicans.
In March, Romney delivered a brutal speech in Salt Lake City where he described the President-elect as a “phoney” and a “fraud”, while also telling Republican voters to cast their primary ballot for whichever other GOP candidate who could beat Trump in their respective states.