Do their voting records reveal them to be anything other than mainstream Republicans? I'll admit that Romney's votes to impeach the man whose endorsement he sought in 2012 were unusually bold,but I can't think of any effect he's had on his party. Quite the opposite actually - at one point Romney claimed he was pro choice, but he's clearly fallen in line. His evolution towards mainstream Republicanism also put him in the comical position of running against the "Romneycare" universal healthcare plan once Democrats adapted it into the Affordable Care Act or "Obamacare".
There's a reason that Romney, McConnell, and Trump share the same party, dysfunctional thought their relationship might be.