Former supporters turn on Romney and embrace the “dog on the roof” meme

This one is a political-nerd thing that requires some back story to it, but:

In the wake of the news that former Massachusetts Governor and 2012 Republican presidential nominee Mitt Romney will likely run for Senate in Utah in 2018, his detractors have resurfaced the old “dog on the roof” smear that still makes no sense to me. The attack is from the 2007 presidential primary Romney lost to John McCain (who went on to lose the election to Barack Obama in the 2008 election) in where a story the Romney’s told about their family trips including their family dog going with them in a dog carrier on the roof of their car being alleged as some kind of horrible thing – evidently by people who have never traveled with dogs in an automobile before (summary: they *don’t* like to be in the cab of a car and much prefer to stick their heads out the window, or, if possible – be in the open bed of a truck during the traveling. A roof dog carrier is like that, except safer).

This one from a reporter at the conservative Washington Free Beacon incomprehensibly depicts the tortured dog meme being a stand-in for “common sense conservatism” riding on Senator Romney’s car down a road of unchecked Trumpism… huh?
https://twitter.com/HashtagGriswold/status/923977076373426177

Romney was a Trump critic who opposed his nomination…but this is alleging that he will speed down the road to no longer check the president at the expense of what is known as “common sense conservatism”?

If you can explain this metaphor to me, please do…