This claim - that 4 million white Conservatives stayed home in 2012 - has never been verified by actual analysis.
There are two reasons to doubt this claim is actually true:
(1) Romney got 1 million MORE votes than McCain.
(2) Obama got 4.5 million LESS white votes in 2012.
Based on that evidence, you could claim that 4.5 million disillusioned white voters rejected Obama in 2012 and stayed home.
One thing that tends to get overlooked in the 2012 analyses (altho it did pop up in a couple threads last week) is that Romney’s GOTV effort collapsed on election day when his GOTV system (ORCA) fell to pieces.
Without there being any sort of backup plan to get a huge chunk of voters out to the polls. Based on the analyses I saw at the time ORCA’s implosion was revealed that, more than any other factor, kept Romney from the Presidency.
I’m hopeful that the new GOTV system the GOP has thrown $100 mil into works. And that the GOP has folks talking to the Brat Campaign, which managed to lay their hands on the Democrat’s GOTV methodology.