Former Massachusetts governor and soon-to be Utah senator Mitt Romney is once again leveling criticism at President Donald Trump. Romney, a Republican, has published an op-ed in the Washington Post titled “The President Shapes the Public Character of the Nation: Trump's Character Falls Short.”

WGBH News contributor David Bernstein has been following Romney’s career, including his successful run for Senate in Utah. Bernstein spoke with WGBH All Things Considered anchor Barbara Howard about the op-ed.

Barbara Howard: Romney just won a U.S. Senate seat in Utah, and he did have Trump's endorsement. Now, he's attacking Trump's character. Did Romney welcome the president's endorsement or did he struggle with it?

David Bernstein: He took the endorsement. He got a lot of questions about it, like, 'Why are you taking the endorsement after criticizing him so badly during the presidential campaign?' But he sort of shrugged it off, saying he’ll take whatever endorsement he can get, and that doesn't mean he'll support everything about him. But clearly, it was an attempt to get in good with some of the Utah Republican base. Trump is not as popular with Utah Republicans as he is in some other places, but you still have to seem to be a little bit pro-Trump, and he did.

Howard: So in that Washington Post opinion piece, Romney says of President Trump, “His conduct over the past two years, particularly his actions last month, is evidence that the president has not risen to the mantle of the office.” Now Romney is due to be sworn in as Utah Senator tomorrow, so why do you think that he had this published on the eve of his swearing-in?

Bernstein: I think in part it was a shot across the bow, to let Trump and his people know that Romney can get attention for negative comments in a way that other senators, certainly other freshman senators, can't do. And also, I think the events of this past month of December bothered Romney in a particular way, because it had to do with our relationship with other countries, how Trump was going about things on the international stage, and he felt he had to speak up about it.

Read more: After Romney Says Trump Has 'Caused Dismay Around The World,' Trump Hits Back

Howard: Other Republicans, as you said, have taken aim at Trump, at least verbally, but most of those have been on their way out, like Senators Jeff Flake or Bob Corker. Romney is just coming into office. Is he going out on a limb here or is he speaking for other current Republican senators?

Bernstein: That’s hard to say. I think he's going off on his own. I think he's trying to stand out, both for the folks back home in Utah and also for sort of the Washington intelligentsia who are paying attention to who they're going to go to for non-Trump opinion on the issues of the day. He wants to stand out among that crowd and I think that he has done that, he's shown that he's the go-to person.

Howard: Do you see Romney's words being backed by action or is it just rhetoric? During the 2016 presidential campaign, Romney did give a searing speech attacking Trump, saying "Donald Trump is a phony, a fraud. His promises are as worthless as a degree from Trump University." But just a few months later, after Trump had won the presidency, Romney came under fire for having dinner with Trump as he was being considered for secretary of state. So where does Romney actually stand? Is he positioning himself as a possible Trump challenger in 2020?

Bernstein: I don't think that he is specifically thinking about 2020 or positioning himself, I think he's positioning himself as a sort of party elder, an important voice for the party. If it turns out that he feels he is needed to take that into the presidential campaign in 2020, I don't think he'd have a problem following through on that. But I don't think he's thinking it now. He's been back and forth on this, trying to pick his spot. I wouldn’t expect real, tangible action, but he will pick his spots where he feels that he has to, and where he feels it will be effective.

Howard: That's WGBH News contributor David Bernstein, talking about former Massachusetts governor Mitt Romney's op-ed in the Washington Post, going after President Donald Trump. Romney is set to take office tomorrow as a Republican Senator from Utah.