Senator-elect Mitt Romney (R-Utah) railed against President Donald Trump’s leadership in a scathing editorial on Tuesday, arguing that the current administration has caused “dismay around the world.”

In a piece published in The Washington Post, Romney, a former Republican presidential candidate, wrote that he felt compelled to comment on the president’s behavior after the departure of several cabinet members and what he called the “abandonment of allies who fight beside us.”

“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 wrote. “His conduct over the past two years, particularly his actions this month, is evidence that the president has not risen to the mantle of the office.”

Romney all but called on the GOP to reject the rhetoric pouring from the White House, noting that he plans to “speak out against significant statements or actions that are divisive, racist, sexist, anti-immigrant, dishonest or destructive to democratic institutions.”

The editorial is the latest in a series of embarrassing rebukes of the Trump administration. Defense Secretary Jim Mattis resigned last month in protest of Trump’s decision to withdraw American troops from Syria and issued a stinging reproach of the president. And former White House chief of staff John Kelly threw water on Trump’s signature campaign pledge for a wall along the southern border as he was preparing to leave the administration.

Bill Clark via Getty Images "I will speak out against significant statements or actions that are divisive, racist, sexist, anti-immigrant, dishonest or destructive to democratic institutions," Romney wrote in The Washington Post.

Romney is just days away from being sworn in as a junior senator in Utah, and some pointed out on Twitter that the op-ed may prime the lawmaker to be a direct challenger in Congress to controversial Trump administration policies. The former Massachusetts governor has flip-flopped on his support for Trump in the past, but he pledged to stand against the president during his Senate bid and speak his mind if he disagreed with White House policies.

This is the best take I've seen so far on Romney's anti-Trump op-ed https://t.co/YXgoQD1ejv — Jonathan Chait (@jonathanchait) January 2, 2019

“I will act as I would with any president, in or out of my party: I will support policies that I believe are in the best interest of the country and my state, and oppose those that are not. I do not intend to comment on every tweet or fault,” Romney wrote Tuesday.

Some expressed cautious optimism about Romney’s op-ed, given his history with Trump.

“I just hope he isn’t another Jeff Flake who says one thing and votes another way,” Rep Ted Lieu (D-Calif.) tweeted.

Others, however, slammed Romney’s piece. Brad Parscale, Trump’s 2020 campaign chairman, fired back on Twitter, calling the editorial “so sad” and attacking the lawmaker’s previous efforts to run for president himself.

“The truth is Mitt Romney lacked the ability to save this nation,” Parscale tweeted. “Jealousy is a drink best served warm.”

The truth is @MittRomney lacked the ability to save this nation. @realDonaldTrump has saved it. Jealously is a drink best served warm and Romney just proved it. So sad, I wish everyone had the courage @realDonaldTrump had. https://t.co/mbxoTqbSX6 — Brad Parscale (@parscale) January 2, 2019