WATCH: Pence Swears in Romney, Says It's 'an Honor'

On Thursday, Vice President Mike Pence (who, as VP, is also president of the Senate) swore in former 2012 GOP presidential candidate and now Sen. Mitt Romney (R-Utah).

"This is an honor," Pence said before administering the oath of office.

Comity between a Republican senator and a Republican vice president would not normally be notable, but Romney wrote an op-ed in The Washington Post slamming President Donald Trump on New Year's Day, just two days before Pence swore him in.

Trump responded with a fiery tweet, declaring, "I won big, and he didn't."

Pence has not yet addressed the bad blood between his boss and the new senator. If any Republican were to primary Trump in 2020, Romney would have the best chance, and it seems reasonable to consider the WaPo article a shot across the bow, testing the waters for a potential challenge.

Romney, a former Massachusetts governor, former Republican presidential nominee, and a man who has sought and won Trump's endorsement twice, is indeed a political force and a moral public servant. Pence rightly considered swearing him in an "honor." It may have behooved him, however, to urge Romney not to consider a primary challenge against President Trump, or at least to respond to the WaPo op-ed.

After the swearing-in, Pence tweeted that it was a "great honor" to "participate in swearing-in ceremonies for members of the US Senate." He made no mention of Romney in particular.

Follow the author of this article on Twitter at @Tyler2ONeil.