??? Why do you suppose the GOP establishment ran John Anderson as a third party candidate? Maybe you weren't around yet, or weren't paying attention. Reagan was attacked for being a trigger happy Cold War cowboy who risked nuclear war with the USSR.
He had Jerry Falwell's newly ascendant Moral Majority behind him, as well as Paul Weyrich's fundraising machine. And to be clear, the democrats did everything they could to make sure everyone knew how conservative Reagan was.
That's how he was attacked, but it never stuck. That's why he was called the Teflon President.