Mitt Romney's announcement Friday that he wouldn't run for president again came as a surprise to many. He was leading in the polls. He and his allies had been sending the message that he was "almost certain" to run again, as one Washington Post headline put it. "Every talk I've had w/ Mitt World leads me to believe he will run," Mark Halperin tweeted Friday morning — just as "multiple sources" told the Daily Beast that Romney was about to announce a third campaign.

But other savvy observers saw Romney's demurral coming. Their secret? They didn't listen to what Romney and his people were saying. Instead, they watched what Republican Party insiders were saying and doing.

The feedback Romney got over the past few weeks was, quite simply, bad

Over the past few years, a group of political scientists has been arguing that party elites play a more important role in guiding the presidential nomination process than they're given credit for. The 2008 book The Party Decides, by Marty Cohen, David Karol, Hans Noel, and John Zaller, makes the case that these insiders heavily influence the process long before the voting begins, in what's called the "invisible primary."

In this phase of the invisible primary, Karol told me last month, "the people who would like to run meet others active in the party — donors, elected officials, other interest groups. They have private conversations, gauge support and see if there's any interest in them running." This is precisely what Romney has spent the past few weeks doing.

But potential candidates' decisions on running aren't based purely on polls, their own instincts, or their beliefs about what’s best for America. Instead, they’re heavily influenced by feedback they are receiving from party insiders — feedback that helps them determine whether they can win.

The feedback Romney got over the past few weeks was, quite simply, bad. His top Iowa staffer from 2008 and 2012 signed on with Jeb Bush. Stories in which former supporters, donors, and prominent Republicans trashed the idea of another Romney run were everywhere. "Mr. Romney was losing important backers, including the New York City hedge fund billionaire Paul Singer, and in the gossipy universe of wealthy Republicans, word was spreading about the defections," the New York Times' Ashley Parker and Jonathan Martin wrote.

party elites were more worth paying attention to than Romney supporters

Political scientists, and people informed by their work, took notice. Back on January 14, Jonathan Bernstein wrote, "This one isn't gonna fly... No one has rallied to Romney’s side other than his core supporters, and reporters are having no trouble finding 2012 supporters who are willing to distance themselves publicly from his third effort." On Thursday afternoon — the day before Romney announced his decision not to run — Bernstein asserted that his campaign "may be dead on arrival."

Through it all, Romney and his team kept signaling that they were moving forward anyway. But there were many reasons to take what his camp was saying with a grain of salt. With Bush and other candidates moving so quickly to lock down donors and supporters, Romney had to act as if he was fully committed if he wanted to remain in the hunt. As for his inner circle, many of them stood to make lots of money if Romney ran again — so they faced obvious financial incentives to hype up that prospect, in hopes of bringing it about.

That's why it was more worthwhile to pay attention to the party elites than Romney supporters. As David Karol wrote at the Washington Post, the lack of insider enthusiasm was Romney's major weakness. "Romney had the poll numbers. He has the money. What he didn’t have was a warm welcome from party elites... It seems he drew conclusions from the signals he got."

Theories like these surely can't explain every idiosyncratic decision politicians make. But overall, the sequence of events is exactly what a reader of The Party Decides would expect. Romney tested the waters. He spent a few weeks calling everyone under the sun to gauge support. And when he didn't get the enthusiastic insider backing he hoped for, he got cold feet. The party made its preferences known — so Romney decided to remain in retirement.