It’s not surprising that Sen. Orrin G. Hatch (R-Utah) is retiring from the Senate. At 83, he’s the longest serving Republican senator in history, and when he won election six years ago, he said it would be his last term.

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But it's also not surprising that President Trump tried to delay this day. Hatch's retirement means the president is losing one of his most fruitful allies in the Senate — and there's a potential he could gain a big enemy in Hatch's place.

It’s only a slight overstatement to say Hatch is the reason Trump ended his first year with a major legislative victory. As chairman of the Senate Finance Committee, Hatch was instrumental in getting Republicans' tax bill to Trump's desk by Christmas, as the president demanded. It was Trump's first (and so far, only) major legislative victory.

Hatch passionately and angrily defended the bill against criticism that it would mainly benefit the wealthy and corporations, drawing headlines for saying stuff like this: “I come from poor people.”

Senate Finance Committee Chairman Orrin G. Hatch (R-Utah) and Sen. Sherrod Brown (D-Ohio) had a tense exchange during a markup of the GOP tax bill on Nov. 16. (Senate Finance Committee)

When the tax bill finally passed on a party-line vote, Trump and Hatch sounded like besties at the celebration at the White House.

“Orrin is a special person,” Trump said.

“Mr. President, I have to say that you're living up to everything I thought you would,” Hatch responded when he got the microphone. “You're one heck of a leader, and we're all benefiting from it.”

Orrin Hatch, Jeff Flake and the no-win scenario GOP senators face with Trump

In addition to supporting the tax bill, Hatch was a key player in urging the Trump administration to drastically shrink two national monuments in Utah. “I asked for the president’s help in fixing this disaster,” Hatch told reporters in Utah in December. “Without hesitation, he looked at me square in the eye and said, ‘We’ll fix it.’ ”

Hatch has even backed the president on the most nagging of issues: the investigation into whether the Trump campaign colluded with Russia to win the election. When news of Donald Trump Jr.'s meeting with a Russian lawyer during the campaign broke, Hatch brushed it off (even though many legal experts said it almost certainly crossed the legal line of collusion). “Look, I know Donald Jr., he's a very bright young man, he's a very nice young man,” Hatch said, adding “... it's impressive to me how dedicated they are to their father.”

No wonder Trump urged Hatch to break his promise and run for reelection. Hatch's relationship with Trump is a rare one in a Senate that has some very vocal critics of the president.

“We hope you will continue to serve your state and your country in the Senate for a long time to come,” Trump said to Hatch in December.

White House responds to news of Sen. Orrin Hatch's (R-Utah) retirement after 42 years in the Senate. (Reuters)

In our rankings of where GOP senators stand on Trump, Hatch leans positive overall. Earlier this year, Hatch was generally supportive of Trump's controversial decision to remove James B. Comey as FBI director, though he did call out the president for not clearly denouncing white supremacists in Charlottesville this summer.

Contrast that with whom could be replacing Hatch in the Senate, and Trump gets an even rawer deal.

None other than Trump’s most long-standing critic in the entire party, Mitt Romney, is reportedly considering a Senate run. During the campaign, Romney, fashioning himself leader of a Republican Party increasingly being hijacked by Trump, said some incredible things about Trump.

The Fix's Aaron Blake pulled together some of Romney's greatest hits:

  • “If we Republicans choose Donald Trump as our nominee, the prospects for a safe and prosperous future are greatly diminished.”
  • “But you say, wait, wait, wait, isn’t he a huge business success? Doesn’t he know what he’s talking about? No, he isn’t and no, he doesn’t.”
  • “Now, Donald Trump tells us that he is very, very smart. I’m afraid that when it comes to foreign policy he is very, very not smart.”
  • “Dishonesty is Donald Trump’s hallmark.”
  • “Think of Donald Trump’s personal qualities: the bullying, the greed, the showing off, the misogyny, the absurd third-grade theatrics.”

If Romney gets into the race, he could win. Romney isn't from Utah, but he has religious and business connections to a state that overwhelmingly voted for him in the 2012 presidential election, and polls suggest voters there still like him a lot.

“Romney would come into the Senate with almost unprecedented power to say whatever he wanted about Trump, should he choose to do so,” Blake points out.

Romney didn't immediately jump into the race, letting Hatch have his day.

Of course, after the campaign, Trump and Romney were photographed dining on frog legs together as Romney campaigned for the secretary of state job.  So, allies and enemies are fungible in politics.

But the way things stand now: Trump will lose one of his most constructive allies in the Senate, possibly replaced by one of his most outspoken critics.