The RNC chair is Mitt Romney's niece. Here's what she said about her uncle's ...

Republican National Committee Chairwoman Ronna McDaniel sided with President Trump over her uncle Mitt Romney, slamming the Utah senator-elect for writing an op-ed in which he criticized the President.

Here's her tweet:

What you need to know about McDaniel: She has been supportive of Trump since the 2016 election and, as the former chairwoman of the Michigan Republican Party, helped Trump win the key state.

She was tapped in December 2016 to succeed Reince Priebus as RNC chair while he took on the White House chief of staff job, from which he was later fired. McDaniel became only the second woman to chair the RNC in history.

Since then, McDaniel has had to navigate the tricky role of being a Trump supporter and Romney's niece. That could continue to prove difficult as her uncle begins his six-year term in Congress on Thursday. The incoming senator has made clear he will support the President where he agrees and speak out when he doesn't.

President Trump said Wednesday he hopes incoming Sen.-elect Mitt Romney will become a "team player" after the Utah Republican decried the President in a Washington Post op-ed.

But by-and-large the President held his fire on the one-time presidential candidate, choosing not to issue any overt insults or criticism of a new congressional foil.

"I wish Mitt could be more of a team player. I'm surprised he did it this quickly. I was expecting something but i'm surprised he did it this quickly," Trump said during a meeting of his Cabinet.

Earlier today, Trump tweeted similar sentiments:

During the Cabinet meeting, Trump noted he'd endorsed Romney in his election, a nod for which Trump said Romney "thanked me profusely."

"I was happy that he won in Utah," Trump said. "I have great popularity in Utah."

And while Trump did not use overly injurious language to hit back at Romney, he did suggest the new senator could have won his own presidential bid if he'd been a little tougher.

"I will say this, if he fought really hard against President Obama like he does against me, he would have won the election," Trump said. "If he fought the way he fights me, I'm telling you, he would have won the election."

In an op-ed published in The Washington Post, Sen.-elect Mitt Romney said President Donald Trump's behavior since taking office "is evidence that the President has not risen to the mantle of the office."

Romney wrote in Tuesday's op-ed that he agreed with some of the policy changes Trump has championed. "But policies and appointments are only a part of a presidency," he wrote.

"It is well known that Donald Trump was not my choice for the Republican presidential nomination. After he became the nominee, I hoped his campaign would refrain from resentment and name-calling. It did not," Romney, the 2012 Republican presidential nominee, wrote in the opinion piece, adding that several of Trump's Cabinet appointments had been "encouraging."

Romney has been a vocal critic of the President during Trump's campaign and first two years in office, although the two had appeared to mend fences after Trump was elected. They were photographed dining together as Trump mulled making Romney his secretary of state, and the President endorsed Romney's Senate bid last year.

Romney is set to take office Thursday.