Former Republican presidential nominee Mitt Romney never actually released his full tax return during the 2012 election cycle, but he's calling on the GOP candidates to do exactly that now.
“One thing I’ll mention is that before I would endorse somebody, I’d want to see their past taxes. We’ve got Cruz, Rubio and Trump -- haven’t released their tax returns. And I’d like to know, you know, have they paid taxes? How much money they made. So we haven’t seen that yet. I’d like to see that. But as we go along here, as the field narrows, I may endorse but that’s not anything immediate.”
I'll go out on a limb and say Mitt Romney's endorsement wouldn't change a thing in this election. The kind of people who ardently support Donald Trump are the kind of people who think Mitt Romney is too liberal.
If Mitt Romney were to endorse Marco Rubio, Cruz and Trump supporters aren't going to change their minds because of it. It's more likely Romney's endorsement would hurt Rubio.