U.S. President Donald Trump and Mitt Romney, the losing 2012 Republican presidential candidate, are sparring, just as Romney is set to claim a Senate seat in the Congress that takes office Thursday.?

In a Washington Post opinion column, Romney declared Wednesday that Trump "has not risen to the mantle of the office" during the first two years of his presidency.

Former Republican presidential nominee Mitt Romney introduces Republican U.S. Rep. Mia Love, of Utah, during a campaign rally, Aug. 24, 2018, in Lehi, Utah.
Romney Attacks Trump, Saying He Causes Dismay Around the World
Mitt Romney, the former Republican presidential candidate and incoming U.S. senator from Utah, sharply criticized President Donald Trump and suggested the U.S.

?"To a great degree, a presidency shapes the public character of the nation," Romney wrote. "A president should unite us and inspire us to follow 'our better angels.' A president should demonstrate the essential qualities of honesty and integrity, and elevate the national discourse with comity and mutual respect. As a nation, we have been blessed with presidents who have called on the greatness of the American spirit. With the nation so divided, resentful and angry, presidential leadership in qualities of character is indispensable.

"And it is in this province where the incumbent's shortfall has been most glaring," Romney concluded.

Sen. Bob Corker, R-Tenn., speaks to reporters at the Capitol in Washington, Dec. 4, 2018.
Departure of Trump's GOP Critics in Senate Leaves a Void
President Donald Trump’s most prominent GOP critics on Capitol Hill are days away from completing their Senate careers, raising the question of who — if anyone — will take their place as willing to publicly criticize a president who remains popular with nearly 9 in 10 Republican voters.Sens. Jeff Flake of Arizona and Bob Corker of Tennessee engaged in a war of words with the president on myriad issues over the past 18 months, generating headlines and fiery tweets from a president who generally insists…

Trump reacted hours after the article was published.

"Here we go with Mitt Romney, but so fast! Question will be, is he a Flake? I hope not," Trump tweeted, referring to another long-time Republican critic, Arizona Sen. Jeff Flake, who declined to seek re-election last year.

Sen. Jeff Flake speaks with reporters before he an
FILE - Sen. Jeff Flake speaks with reporters in Washington, Nov. 14, 2018.

"Would much prefer that Mitt focus on Border Security and so many other things where he can be helpful," Trump said on Twitter.   

?Later, Trump told his Cabinet that if Romney had fought former President Barack Obama in the 2012 election like he did him, Romney would have won.

Romney's attack on Trump also drew a rebuke from the chairwoman of the Republican National Committee, Ronna Romney McDaniel, a niece of the new senator.

She said Trump "is attacked and obstructed" by the mainstream news media and Democrats on a daily basis. "For an incoming Republican freshman senator to attack @realdonaldtrump as their first act feeds into what the Democrats and media want and is disappointing and unproductive."

Romney later told CNN he doesn't always disagree with the president. There "are places where we agree on a whole series of policy fronts, but there are places that I think the president can, if you will, elevate his game."

He also didn't say whether he would endorse Trump in 2020. "I'm going to wait and see what the alternatives are," he said. But he did rule out challenging Trump himself.

Romney and Trump have carried on a love-hate relationship over the last several years.

Romney called Trump a "phony" and a "fraud" during the 2016 presidential campaign, although Trump later briefly considered nominating the one-time Massachusetts governor for secretary of state, as he shaped his new government.

Trump bypassed Romney, but last year endorsed his Senate candidacy in the western state of Utah.

In the column, Romney, who easily won his election, said as he becomes a senator, "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. But I will speak out against significant statements or actions that are divisive, racist, sexist, anti-immigrant, dishonest or destructive to democratic institutions."