A much stronger Libertarian current ran in the party in 2012, and that favored fiscal conservatives rather than cultural conservatives. Remember, Paul Ryan was acclaimed by the grassroots and was a popular pick among conservatives for his pretty radical budget ideas at the time rather than being demonized as a globalistopenborderskochfundedcuck or whatever the hell the people at Breitbart are saying now.
The very strongly conservative views on economics came perhaps as a reaction to both Obama and OWS, just as the conservative base currently is very strongly conservative on the border issue after the 2014 Central American migrant surge and the European migrant crisis.
Trump would have had a market in 2012 for border hawkishness, as there is always a market for that, but it wasn't a disqualifying issue nor was it a particularly important one in 2012, considering the acceptance of Paul Ryan, Ron Paul's primary run, and Mitt Romney being attacked for being not enough on the side of business. The birtherism thing was also something that most people, regardless of your views, thought was ridiculous and would not get behind. Birtherism had a peak, in mid 2009, as the Tea Party rallies got a bit out of hand, but it afterwards was discredited and even the most populist voices on the right like Limbaugh and Hannity called it out as dumb.