WASHINGTON (Reuters) - U.S. President Donald Trump rebuffed sharp criticism from fellow Republican Mitt Romney on Wednesday, heaping scorn on the incoming senator in a sign of tensions to come in Washington even before a new Congress is officially sworn in.

Romney, who starts work on Thursday when members of the 2019-2020 Congress take office, suggested in a newspaper essay published on Tuesday that Trump had “caused dismay around the world” and said his presidency had “made a deep descent in December.”

“On balance, his conduct over the past two years ... is evidence that the president has not risen to the mantle of the office,” said Romney in the Washington Post essay, reprising a strong critique of Trump that he voiced during the 2016 presidential campaign.

Trump responded with a tweet on Wednesday, noting Romney’s failed 2012 White House bid and also taking a shot at former Republican Senator Jeff Flake, who has just retired from Congress and who has been one of the few Republican lawmakers to be openly critical of the president.

“Here we go with Mitt Romney, but so fast! Question will be, is he a Flake? I hope not. Would much prefer that Mitt focus on Border Security and so many other things where he can be helpful. I won big, and he didn’t. He should be happy for all Republicans. Be a TEAM player & WIN!” Trump wrote on Twitter.

Trump repeated this theme later during a cabinet meeting, saying he wished Romney could be more of a “team player.”

The president, a businessman and television star with no prior government experience, caused deep divisions in the party when he won the Republican White House nomination and then the election in 2016, upending party orthodoxy on foreign policy, deficits and other issues and governing in sometimes turbulent style.

But public criticism from Republican lawmakers has been rare. It was unclear whether any other prominent members of the party would feel emboldened to criticize Trump ahead of his presumed 2020 re-election bid, or whether the president will face any serious challengers for the party’s White House nomination.

‘SOUR GRAPES’

FILE PHOTO: Mitt Romney arrives at the Metropolitan Museum of Art Costume Institute Gala (Met Gala) to celebrate the opening of “Heavenly Bodies: Fashion and the Catholic Imagination” in the Manhattan borough of New York, U.S., May 7, 2018. REUTERS/Carlo Allegri/File Photo

Senator Rand Paul, a conservative Republican, took Romney to task on a conference call. “You’ll find the vast majority (of Republican lawmakers) will wish he hadn’t said it,” said Paul.

Brushing aside the fact that Trump often personally attacks and insults other politicians, Paul said Romney’s criticism of the president’s character was a “big mistake” and an attempt by the new senator to present himself as “holier than thou.”

“Some might say it’s sour grapes at not having won the (presidential) post himself,” said Paul. He added: “I don’t think there’s an appetite for a Romney run (for president) in the Republican Party.”

Republican National Committee Chair Ronna McDaniel also criticized Romney, saying on Twitter his essay was an attack on Trump that was “disappointing and unproductive.”

McDaniel is a niece of Romney. Seven years ago, Romney was the party’s presidential nominee, running with Paul Ryan, who retired from Congress last month. Romney lost to then incumbent Democratic President Barack Obama.

Paul also took a run at the presidency. He dropped out early in 2016 from the Republican primary race that Trump won.

Representatives for Romney could not be immediately reached for comment on the tweets and remarks by Trump, Paul and McDaniel.

Romney and Trump traded barbs during the 2016 campaign, with Romney calling Trump a “fraud” and Trump slamming Romney’s 2012 loss. The two later appeared to bury the hatchet, with Trump briefly considering Romney to be his secretary of state and endorsing Romney’s 2018 run for the Senate.

But in Tuesday’s essay, Romney wrote of Trump, “The appointment of senior persons of lesser experience, the abandonment of allies who fight beside us, and the president’s thoughtless claim that America has long been a ‘sucker’ in world affairs all defined his presidency down.”

He promised to speak his mind in Washington, which will now feature a divided Congress as Republicans retain a majority in the Senate and Democrats take control of the House of Representatives, after Republicans lost their House majority in November’s elections.

“I will speak out against significant statements or actions that are divisive, racist, sexist, anti-immigrant, dishonest or destructive to democratic institutions,” Romney wrote.