SALT LAKE CITY — Sen. Orrin Hatch, R-Utah, announced Tuesday he is retiring at the end of his term, finally ending speculation about whether this would be his final year in office and opening the door for a run by Mitt Romney.

"I've always been a fighter," Hatch said in a video announcement posted on YouTube and tweeted shortly before noon. "But every good fighter knows when to hang up the gloves. And for me that time is soon approaching."

He then said "after much prayer and discussion with family and friends, I've decided to retire at the end of this term." Hatch had spent the holidays with his family in Utah, debating what to do.

Before making his decision public, Hatch assembled the staff in his Salt Lake office to let them know first. With his Washington, D.C., office watching via video conference, he delivered the news.

The mood was "quite somber," said his spokeswoman of nearly 24 years, Heather Barney. "No one knew. I couldn't have told you even this morning for sure what I thought would happen."

The decision was a difficult one for Hatch, she said, and bittersweet for those around him who were happy to see him "going out on top" but also aware of how hard it is for him to leave a lifetime of service.

"It kind of takes your breath away a little bit," Barney said. "He really is still a fighter. That's why it's hard. He's not really slowed down. He has the grit and determination you don't see really very often in people."

In his video, he describes his childhood "during the Great Depression, living in a ramshackle house," and that "only in a nation like ours could someone like me — the scrappy son of a simple carpenter — grow up to become a United States senator."

Hatch cites his accomplishments during more than four decades in the Senate, including authoring more bills that have become law than any living member of Congress.

He said he has played a central role in major legislation and in the confirmation of every current member of the U.S. Supreme Court, but called the Religious Freedom Restoration Act one of his proudest achievements.

Hatch was first elected to the Senate in 1976, after convincing voters the three-term Democratic incumbent had served too long. Now 83, he had promised during his last campaign six years ago that he wouldn't run again.

But then Hatch began raising the possibility of one more term. He is chairman of the powerful Senate Finance Committee, a position he could hold for two more years, and Senate president pro tempore, third in the line of presidential succession.

Hatch is the most senior Republican in a GOP-controlled Senate and has worked closely with President Donald Trump to pass the party's tax-cutting plan and on shrinking Utah's Bears Ears and Grand Staircase-Escalante national monuments.

It was Hatch who invited Trump to come to Utah in December to announce he was making significant reductions in the monuments set aside by past Democratic presidents, and to meet with LDS Church leaders.

Trump praised Hatch in a speech at the Utah Capitol and urged him to stay in office.

Congratulations to Senator Orrin Hatch on an absolutely incredible career. He has been a tremendous supporter, and I will never forget the (beyond kind) statements he has made about me as President. He is my friend and he will be greatly missed in the U.S. Senate! pic.twitter.com/0VjzLEeHTl — Donald J. Trump (@realDonaldTrump) January 2, 2018

Romney, the GOP's 2012 presidential nominee and popular in the state he now calls home, has been one of Trump's toughest critics. He is said to be putting together a campaign, but has not talked publicly about his plans.

White House press secretary Sarah Huckabee Sanders said Tuesday the president "certainly has the greatest and deepest amount of respect for Sen. Hatch" and his experience, including the "massive effort" to get the tax reform plan passed.

Trump "praises his service and is very sad to see Sen. Hatch leave and knows that he will certainly be missed," she said. Asked if the president would support Romney for the Senate, Sanders said she hasn't "had that conversation" with the president.

Romney was initially encouraged by Hatch to get in the race. The length of time Hatch has taken to finally decide about 2018 has been seen as keeping other candidates from considering a run.

On Facebook Tuesday, Romney referred to Hatch as his friend and thanked him for his service.

He pointed out that Hatch is "the longest-serving Republican senator in U.S. history," and said he has "represented the interests of Utah with distinction and honor."

But Romney said nothing about the Senate race in his post.

I join the people of Utah in thanking my friend, Senator Orrin Hatch for his more than forty years of service to our... Posted by Mitt Romney on Tuesday, January 2, 2018

Derek Miller, who has looked at running for the Senate seat, said he expects Romney to get in the race quickly.

"I think before the end of this week you'll see Gov. Romney running. He'd be smart to make an announcement sooner rather than later," Miller said. "The longer he waits, the more chaos it facilitates."

Miller, a former chief of staff to Gov. Gary Herbert and now president and CEO of the World Trade Center Utah, said he will be "fully supportive" of a Romney run and step aside.

Miller said he wasn't surprised by Hatch's choice to retire.

"As time has gone on, especially the last couple of weeks, it's been increasingly clear he was going to keep his promise," he said. Going home for the holidays "was probably the deal clincher for him."

Not only did Hatch get to be reminded "there is a life outside of Washington, D.C.," he can leave the Senate knowing he "accomplished exactly what he set out to accomplish, which is this historic tax reform," Miller said.

Now, Hatch can "walk off the field after winning the Super Bowl and call it good," he said. "Not many people get to walk out on top. He's one of them."

Chris Karpowitz, co-director of the BYU Center for the Study of Elections and Democracy, said the announcement from Hatch represents a huge shift in Utah politics.

"There are many Utahns who have only known Orrin Hatch as one of their senators. So this is a big moment. It's a momentous decision," Karpowitz said, that clears the path for what he expects will be a Senate bid from Romney.

Anyone else who gets in the race would have work to do introducing themselves to voters, he said. The Democrat already in the race, Salt Lake County Councilwoman Jenny Wilson, formally launched her campaign last September.

"That's the huge advantage Mitt Romney has. He's already well-known and many, many people in Utah have already cast a ballot for him as president," Karpowitz said. "That sort of attention and name recognition is extremely valuable."

Kirk Jowers, a longtime Romney supporter, said he is "very optimistic that Mitt Romney will be our next senator. He has a real passion to serve. He sees a void, I think, on a number of levels that he can fill by serving as senator from Utah."

Jowers, former head of the University of Utah's Hinckley Institute of Politics, said political insiders already see Romney as a candidate.

"The assumption in the political world is Mitt is running and people are pretty happily deferring to him," he said, adding that Romney is waiting to make his intentions public because he "is unfailingly a class act."

Romney "is eager to give Sen. Hatch his due" out of genuine respect for his accomplishments, Jowers said. "That's why he was never going to impede on Sen. Hatch's timing on making this announcement."

Hatch made national headlines Tuesday and a Romney Senate campaign would likely do the same. Former White House chief strategist Steve Bannon has already gone after Romney and his Mormon faith during the recent Senate race in Alabama.

Romney had said electing Roy Moore, Bannon's pick in the special election despite accusations of sexual misconduct with teenage girls years ago, would be a stain on the GOP and the nation.

Moore denied the charges but lost the special election to a Democrat, Doug Jones. Jones is the first Democrat to represent Alabama in the Senate in a quarter of a century.

Bannon responded at a Moore campaign rally by accusing Romney of having "hid behind your religion" to avoid the draft during the Vietnam War by serving an LDS mission in France "while guys were dying in rice paddies in Vietnam."

Utah leaders jumped into the fray, with the governor calling Bannon a "Mormon bigot” and urging Bannon to "stay out of Utah. We don’t need you. We don’t want you. You don’t line up with American values. You don’t line up with Utah values."

Jowers said Bannon "would be a fool to get involved here. Everyone in Utah knows Mitt Romney and they've proven they've loved him through the past presidential campaigns as well as his Olympic stewardship" as head of the 2002 Winter Games.

Karpowitz said the race will attract national attention because of how Hatch and Romney view the president.

"They'll watch it not because Mitt Romney's policies will be dramatically different from Orrin Hatch's, but stylistically, there could be significant differences," he said. "No where is that more evident than their relationship with Donald Trump."