But the connection that rankles her critics the most is not a campaign hire or an endorsement; it's the timing of a viral video of presumptive Democratic nominee Representative Bruce Braley speaking derisively about farmers to a group of lawyers on the same day as Ernst's "squeal" ad was released.
America Rising, a Republican opposition research group headed by former Romney 2012 campaign manager Matt Rhoades, helped turn a once-sleepy race into a marquee contest with that video, which came out just as Ernst launched the TV ad that helped drive her campaign to the top of the GOP primary polls.
To Ernst opponents, the coincidental timing didn't pass the smell test. Ernst's hog-castration ad ran only on Des Moines cable channels, but it received national attention in part because Braley's gaffe had shone a spotlight on the race.
"I don't believe in coincidence," said Iowa GOP operative Christopher Rants, who supports a different Republican running in the Senate primary, Mark Jacobs. "Look at the people who run America Rising, the timing of the release of the Braley video, which was immediately picked up by Romney activists here in Iowa who are supporting her, and 48 hours later here's Joni in the hog barn."
How Mitt Romney got the ball rolling for Joni Ernst's Senate bid
Click on the circles in the timeline for more information. Red circles include videos.
Both America Rising and Ernst's campaign deny any coordination. A timeline of the GOP field's responses appear as though her rival businessman Mark Jacobs may have been the first candidate aware of the video (which floated around among Republicans for several days before it was published online) putting out a statement rapidly after it was released.
Romney's alumni are also sprinkled throughout the campaigns of Ernst's competitors as well. America Rising staffers have close ties with both Jacobs and former U.S. Attorney Matt Whitaker's campaigns.
But Ernst is Romney's personally chosen candidate, whom he endorsed three weeks before any of her other major nods.
"I tell you, in Washington, if you want them not just to squeal, but if you want real change, you want someone to shake things up, Joni Ernst will shake things up in Washington," Romney told a crowd of Ernst supporters in Cedar Rapids on Friday, according to the Des Moines Register.
Along with Iowa Governor Terry Branstad, Romney helped give the candidate an early boost that put her in a good position for national attention—including the Chamber of Commerce's endorsement and support from the Senate Conservatives Fund, which often stands opposed to the Chamber in primaries—that rolled in after the Braley video. The influential Branstad had made clear before the Republican primary began that he wanted to help elect a first female candidate to federal office in the Hawkeye State's history, and both Ernst and Branstad had endorsed Romney in his own election.