This post has been updated now that Hatch has announced his retirement. There had been some uncertainty in recent weeks about Hatch's intentions, but he made it official Tuesday.

The Fix’s Amber Phillips explores the potential ramifications of the upcoming retirement of Sen. Orrin G. Hatch (R-Utah.). (Bastien Inzaurralde/The Washington Post)

Mitt Romney's path to a U.S. Senate seat just cleared up, and now he's on a collision course for President Trump.

Sen. Orrin Hatch (R-Utah) announced Tuesday that he will not seek reelection in 2018, and Romney is expected to run to succeed him. After publicly weighing a repeat presidential bid in 2016, then publicly denouncing Trump, then unsuccessfully seeking to become Trump's secretary of state, Romney's interest in the Senate became apparent.

Romney, of course, served as governor of Massachusetts, not Utah. But his Utah bona fides are crystal clear -- starting with his stewardship of the 2002 Salt Lake City Olympics -- and he'd almost undoubtedly waltz into the Senate if he ran. While it's still early and other candidates could be tempted to give it a shot, this is a guy who won Utah by 48 points in the 2012 presidential election and polls show remains astoundingly popular there. A recent survey showed 71 percent of Utahns viewed him favorably.

But one person who should be watching this with particular concern is Trump.

Basically no Republican criticized Trump as harshly as Romney did on the 2016 campaign trail. Yes, Romney then sought to lead Trump's State Department and said some nice things about Trump, but he was turned down for that job, which may make the fire burn even hotter.

And most importantly, unlike other Republicans in red states, Romney wouldn't necessarily feel the need to temper his opposition to Trump in the Senate. Utah is about equally as anti-Trump as it is pro-Romney. Trump did win the state, but that victory owed almost entirely to the state's Republican lean. Polls there showed Trump's favorable rating as low as 19 percent and his unfavorable rating as high as 71 percent, largely thanks to Mormons disliking him.

White House press secretary Sarah Huckabee Sanders wouldn't say if President Trump is open to supporting Mitt Romney for Sen. Orrin Hatch's Utah Senate seat. (Reuters)

GOP senators like John McCain (Ariz.), Bob Corker (Tenn.), Jeff Flake (Ariz.) and Ben Sasse (Neb.) have certainly been willing to break with Trump publicly on certain things, but they also have pro-Trump constituencies back home to worry about. Most every Republican who has criticized Trump has seen his numbers tank with the GOP base.

And their criticisms have never really been of the sort that Romney offered in 2016. A sampling of what Romney offered:

  • “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.”

These comments were offered in the midst of a primary campaign in which Romney wanted someone else to win. And plenty of other Republicans said really bad things about Trump at the time before coming around, endorsing him and trying to make the most of their new Trump realities. But Romney never did — at least, not until he thought he could affect the Trump administration from within.

Trump's numbers in Utah have improved since the 2016 campaign, but they remain soft, and Romney's credibility with the GOP base there provides him a unique opportunity to go head-to-head with Trump, should he decide to do so. He would also do so in what is likely to be a pretty closely divided Senate, where one vote can matter greatly (as we've discovered frequently over the last year).

And in our highly partisan era, it could be a completely unusual and potentially must-see political dynamic.