I think McCain had full support after Romney realized he was close to getting mathematically eliminated from winning on the first ballot and ended his campaign.
He announced it at CPAC.
Romney didn’t clinch till late May 2012
Santorum who was in the seat Cruz is in now dropped out long before
Ditto 2008 with McCain and Romney
But Fox and GOPe and Talk Radio especially Rush have a new rationalization
Because it suits them