"There were people walking into election week 2012 that thought we were going to win Pennsylvania, and for sure we were going to win Ohio and, for sure, were were going to win Florida and the polling was just really, quite frankly, off," Walsh told CNN's "Party People" podcast hosts Kevin Madden and Mary Katherine Ham in a conversation less than a week before Election Day.
In 2012, President Barack Obama went on to win Ohio, Pennsylvania and Florida as well as a lot of other states for a grand total 332 electoral college
votes, far above the votes needed to defeat Romney and win re-election.
Walsh said the party has learned lessons from that loss eschewing a reliance on polling for a more predictive modeling program called "voter scores," which gives each would-be voter in the 190-million member voter file a numerical value, 1-100, on how likely they are to vote and how likely they are to vote Republican.
"The beauty of predictive modeling is you're watching an electorate voter-by-voter over a long period of time," Walsh said. "You're watching their movement, you're watching what they care about, you're watching what they respond to to and there are a lot of upsides to this."
Walsh highlighted success of their efforts in the 2014 midterms -- particularly the North Carolina Senate race where Thom Tillis defeated incumbent Democrat Kay Hagan, despite polls showing the opposite result.
As for this year's race, Walsh said the RNC's goal is to focus on being the voter turnout infrastructure for Donald Trump's presidential campaign, which Walsh described as originally comprising of "10 guys and a Twitter account."
Walsh said her takeaway from the RNC's data, which is not publicly shared, is how much voters don't want to vote for Democratic presidential nominee Hillary Clinton. Voters are looking for any reason to vote for someone else, she said.
"I think another thing that we've seen is that when Mr. Trump stays on message, people come home real quick," Walsh said.
"That's usually only for about five minutes," Madden responded.
"Let's give him 45 minutes," Ham added.
To hear what Walsh thinks will be Trump's lasting impact on the Republican party, her Show Me state roots and what's the key piece of data she's looking for going into Election Day, listen to CNN's "Party People" podcast.
Get CNN's "Party People" podcast at CNN