Utah Senator-elect Mitt Romney had some strong words for Donald Trump in a blistering op-ed published this week where he said 'the president has not risen to the mantle of the office'.

The 71-year-old Republican, who was the GOP presidential nominee in 2012, revealed he's highly critical of Trump's two years in office.

'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,' he wrote in an op-ed piece for the Washington Post published Tuesday.

'When he won the election, I hoped he would rise to the occasion. His early appointments of Rex Tillerson, Jeff Sessions, Nikki Haley, Gary Cohn, H.R. McMaster, Kelly and Mattis were encouraging. But, on balance, 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 added.

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Utah Senator-elect Mitt Romney, 71, penned a harsh critique of Trump in the Washington Post on Tuesday and will be sworn into Congress on Thursday. He says he will speak out against Trump's hateful and derisive comments

Romney said that policy is only part of the president's job. The nation's leader must also be honest, of integrity, and bring the nation together, which Romney says Trump has failed to do. He shared the above tweet with a link to the op-ed Tuesday

He said that Trump's job in the White House and as the nation's leader is to 'demonstrate the essential qualities of honesty and integrity', something he has failed to do.

'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 wrote.

He added that America's reputation as a global leader has also plummeted following Trump's presidency.

'Trump’s words and actions have caused dismay around the world. In a 2016 Pew Research Center poll, 84 percent of people in Germany, Britain, France, Canada and Sweden believed the American president would "do the right thing in world affairs." One year later, that number had fallen to 16 percent,' he said.

The former Massachusetts governor said Trump 'has not risen to the mantle of the office' and he intends to defy the president if he makes 'divisive, racist, and anti-immigrant' comments. Trump and Romney pictured together at the Trump Golf Club in New Jersey in 2016

He shared his opinion piece just two days before he'll be sworn in as Senator

However, he noted that some of Trump's policy decisions during his time in office have been worthy of applause.

He praised his corporate taxes, the end of excessive regulations, the crack down on China's international trade practices, his criminal justice reform, and the appointment of conservative judges - hot button issues that Republicans have rallied behind for years.

Romney, the former Massachusetts governor, will be sworn into the Senate on Thursday and says that he will speak out against Trump's wrongdoings while in office.

He promised to counter Trump's statements that are divisive and combative.

'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,' he said.

'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,' he added.

He added that he looks forward to his term as senator and working with Republican Senate Majority Leader Mitch McConnell and the rest of Congress.