Gabriel called the timing of Romney's attack very important, coinciding with the reality of the GOP's problems and Trump's stature.
"This is something that wouldn't have happened a year ago. Nobody would have taken on President Trump," Gabriel said. "He is very much more vulnerable and he knows this."
He also thinks Trump's response to Romney was gentler than it would have been several months ago.The president first tweeted Wednesday morning that he would prefer Romney focus on the border wall and other things.
"I won big and he didn't. He should be happy for all Republicans."
Then later in the afternoon, Trump addressed the issue in his first Cabinet meeting of the year. "I wish Mitt could be more of a team player. I'm surprised he did it this quickly," said Trump, who pointed out that he endorsed Romney in the Senate race and the candidate "thanked me very profusely."
"If he fought really hard against President Obama like he does against me, he would have won the election" in 2012, Trump added.
Romney has criticized the president in the past, calling Trump a "fraud" and "phony" in 2016.